Different possible configurations of two nitrogen-adatoms on graphene are studied using density functional theory. Adsorption of single nitrogen atom on the bridge site of graphene is accompanied by distortion of the sheet. Electronically, this case amounts to p-type doping. Two N atoms adsorbed on the graphene sheet can share a bond in two ways. They acquire positions either just above two adjacent carbon atoms or they form a bridge across opposite bonds of a hexagon in the sheet. Both these configurations also induce structural distortion of the sheet. Another stable configuration consists of two N atoms bonded as an N_{2} molecule physisorbed on the graphene sheet. It is also possible to adsorb two N atoms on opposite sides of the graphene sheet, bonded to the same two C atoms. Moreover, two N atoms can be individually adsorbed on alternate bridge sites of neighboring hexagons experiencing a repulsion, the energy for which arises from the additional distortion of the graphene sheet. The densities of states near the Fermi level are found to be dependent on the adsorption configurations of two nitrogen atoms on graphene. Thus the electronic properties of graphene can be controlled by the selective adsorption of two nitrogen atoms. © 2014 Wiley Periodicals, Inc.

Understanding the details of the interaction of atomic nitrogen impurities with graphene is very important for optimizing the graphene doping process and control the process of incorporation of nitrogen in the sheet, which in turn affects the electronic properties of the material. Theoretical calculations allow the exploration of various configurations for two nitrogen adatoms on graphene, and estimate their relative structural stability and electronic structure.

Here, we consider a class of generalized linear chains; that is, the ladder-like chains as a perturbation of a 2*n* path by adding consecutive weighted edges between opposite vertices. This class of chains in particular includes a big family of networks that goes from the cycle, unicycle chains up to ladder networks. In this article, we obtain the Green function, the effective resistance, and the Kirchhoff index of ladder-like chains in terms of the Green function, the effective resistance, and the Kirchhoff index of the path. © 2014 Wiley Periodicals, Inc.

In the context of organic Chemistry, it is of interest to have good parameters that can discriminate between molecules with similar shape but different structural properties. In recent years, some new parameters have been considered, for instance, effective resistances and Kirchhoff index (the sum of the effective resistances). In this work, a closed formula for the Kirchhoff index of some (molecular) graphs is presented by reinterpreting these graphs as perturbation of a path.

In this article, based on the former accurate and precise *ab initio* calculation results for potassium nitride (KN) and calcium nitride (CaN), I revisit the possibilities and potentials of KN and CaN as the best candidate for molecular multiple quantum bit (MMQB) for the diatomic molecular quantum computer (DMQC), and would like to propose the two molecules as CPUs of the DMQC. Lowest lying four electronic states of CaN are energetically located within 1800 cm^{−1}. These four states form the good molecular electronic two quantum bits through the dipole and weak spin–orbit interactions. ^{3}Π state of KN is calculated to lie above ground ^{3}Σ^{−} state by 177 cm^{−1}. KN is a promising candidate for an electronic one quantum bit. When vibrational progression is considered to be accompanied by the electronic transition, CaN and KN are good candidates for larger MMQBs up to a thousand even in the single molecule because the concrete quantum state bearing the quantum bit is each molecular ro-vibronic state, that is, the specific rotational state on each vibronic level. When CaN and KN work in assemblies as quantum bit, those assemblies become larger MMQBs, the number of which might reach the Avogadro number because the molecular spectra appearing in the molecular spectroscopy are the results from the observation by the photon-exchange among intramolecular quantum states made up of 10^{15} to the Avogadro (6.02 × 10^{23} mol^{−1}) number of molecules interacting with radiation. Even without the vibrational progression, in the case of the lowest two quantum bit of KN, which is a stable vibronic two quantum bit, a thousand of KN molecules provide a thousand of MMQBs. That is the same situation as that for CaN. Using KN and CaN as MMQBs (playing the triple roles of CPU, RAMs (memory), and storages) ultra-fast “in core” quantum computation can be done. An application of the full-CI quantum chemistry calculation results for the demonstration of the DMQC is discussed. I strongly hope that the MMQB will “oscillate” and that the DMQC will be realized in the near future for the welfare of human being and the further development of modern material civilization. © 2014 Wiley Periodicals, Inc.

The potential of KN and CaN as molecular multiple quantum bit for diatomic molecular quantum computers (DMQC) are investigated and supported in this work. Full-CI quantum chemistry calculations of large biological systems are imagined as goal for the realization of DMQC and its application in chemical modeling.

When an external, time-dependent field interacts with a molecular system various phenomena may take place. However, concentrating on a region close enough to a point of conical intersection, we find that this external field builds up a field similar to an electromagnetic field formed on the one hand by Field-Dressed nonadiabatic coupling terms which are reminiscent of the Maxwell–Lorentz Vector potentials, and on the other hand via a scalar potential formed by the dipole-interaction with an external field. In this article, we show that this new field, to be termed Molecular Field, is characterized by several spatial and space-time Field-Dressed Curl equations and one, single, space-time Field-Dressed Divergence equation. These equations are then shown to yield, just as in the general theory of electromagnetism, the corresponding Field-Dressed Wave Equations. This achievement could be materialized employing the (1,2) antisymmetric matrix elements of any of the 2×2 dimensional Field-Dressed nonadiabatic coupling matrices. © 2014 Wiley Periodicals, Inc.

The interaction between the Born Oppenheimer non-adiabatic coupling terms (NACT) and an external electromagnetic field, at the vicinity of a conical intersection, is treated. It is shown that such an interaction results in a Wave Equation, for each component of the NACTs:

In these equations c is the velocity of light, is the time-dependent potential exerted by the dipole interaction with an external field and p and q are any two Cartesian coordinates (the extension to a larger number of coordinates is straightforward).

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When an external, time-dependent field interacts with a molecular system various phenomena may take place. However, concentrating on a region close enough to a point of conical intersection, we find that this external field builds up a field similar to an electromagnetic field formed on the one hand by Field-Dressed nonadiabatic coupling terms which are reminiscent of the Maxwell–Lorentz Vector potentials, and on the other hand via a scalar potential formed by the dipole-interaction with an external field. In this article, we show that this new field, to be termed Molecular Field, is characterized by several spatial and space-time Field-Dressed Curl equations and one, single, space-time Field-Dressed Divergence equation. These equations are then shown to yield, just as in the general theory of electromagnetism, the corresponding Field-Dressed Wave Equations. This achievement could be materialized employing the (1,2) antisymmetric matrix elements of any of the 2×2 dimensional Field-Dressed nonadiabatic coupling matrices. © 2014 Wiley Periodicals, Inc.
The interaction between the Born Oppenheimer non-adiabatic coupling terms (NACT) and an external electromagnetic field, at the vicinity of a conical intersection, is treated. It is shown that such an interaction results in a Wave Equation, for each component of the NACTs:In these equations c is the velocity of light,
Φ∼(p,q|t) is the time-dependent potential exerted by the dipole interaction with an external field and p and q are any two Cartesian coordinates (the extension to a larger number of coordinates is straightforward).
Investigation of dephasing in an open quantum system under chaotic influence via a fractional Kohn–Sham scheme http://onlinelibrary.wiley.com/resolve/doi?DOI=10.1002%2Fqua.24735Investigation of dephasing in an open quantum system under chaotic influence via a fractional Kohn–Sham scheme Timothy Ganesan 2014-07-12T06:29:54.70522-05:00 doi:10.1002/qua.24735 John Wiley & Sons, Inc. 10.1002/qua.24735 http://onlinelibrary.wiley.com/resolve/doi?DOI=10.1002%2Fqua.24735 Full Paper n/a n/a

In this work, the dynamics of dephasing (without relaxation) in the presence of a chaotic oscillator is theoretically investigated. The time-dependent density functional theory framework was used in tandem with the Lindblad master equation approach for modeling the dissipative dynamics. Using the Kohn–Sham (K–S) scheme under certain approximations, the exact model for the potentials was acquired. In addition, a space-fractional K–S scheme was developed (using the modified Riemann–Liouville operator) for modeling the dephasing phenomenon. Extensive analyses and comparative studies were then done on the results obtained using the space-fractional K–S system and the conventional K–S system. © 2014 Wiley Periodicals, Inc.

The dephasing of interacting many-electron systems under chaotic influence is an unexplored complex phenomenon. An effort toward a more complete theoretical understanding of its dynamics is performed using fractional formulations. Using this approach, some interesting insights are uncovered and these findings are examined in detail.

Methyldiazonium ion ( ) is an ultimate carcinogen that can methylate multiple sites in DNA/RNA. In present contribution, density functional theory calculations using the B3LYP and M06-2X functionals and the 6-31G(d,p) and aug-cc-pVDZ basis sets are carried out to study methylation reactions of at the different nucleophilic sites of DNA/RNA bases and their nucleosides. Total 12 nucleophilic sites, that is, the N2, N3, N7, and O6 sites of guanine; the N1, N3, N6, and N7 sites of adenine; O2 and N3 sites of cytosine and the O2 and O4 sites of thymine and uracil have been considered for study. Thus, a total of 30 reactions have been studied here. The polarizable continuum model is used for solvation calculations. The N7 site of guanine, N7(G), is found to be most reactive in all the reactions studied here, which is in agreement with experiment. However, the calculated reactivity of toward the N7(G) site in aqueous media follows the order: guanine > deoxyguanosine > guanosine. The reactivities of many other sites including the O6(G), O2(C), and N3(A) sites are also modified in going from DNA/RNA bases to their nucleosides and from DNA to RNA nucleosides. Thus, we note that the presence of sugar moiety significantly modifies the methylation pattern of bases caused by . © 2014 Wiley Periodicals, Inc.

The alkylation reaction of DNA and RNA is of particular interest as it has been linked to mutation and cancer. Alkylation patterns depend on the alkylating agents, the position in DNA/RNA and on whether DNA is single- or double-stranded. Density functional theory calculations show how the methylation pattern of bases in DNA nucleosides differs from those in RNA nucleosides when they are exposed to methyldiazonium ion

While the formalism of multiresolution analysis, based on wavelets and adaptive integral representations of operators, is actively progressing in electronic structure theory (mostly on the independent-particle level and, recently, second-order perturbation theory), the concepts of multiresolution and adaptivity can also be utilized within the traditional formulation of correlated (many-particle) theory based on second quantization and the corresponding (generally nonorthogonal) tensor algebra. In this article, we present a formalism called scale-adaptive tensor algebra, which introduces an adaptive representation of tensors of many-body operators via the local adjustment of the basis set quality. Given a series of locally supported fragment bases of a progressively lower quality, we formulate the explicit rules for tensor algebra operations dealing with adaptively resolved tensor operands. The formalism suggested is expected to enhance the applicability of certain local correlated many-body methods of electronic structure theory, for example, those directly based on atomic orbitals (or any other localized basis functions in general). © 2014 Wiley Periodicals, Inc.

A formalism called scale-adaptive tensor algebra (SATA) introduces an adaptive representation of tensors of many-body operators via the local adjustment of the basis set quality. SATA is expected to enhance the applicability of certain local correlated many-body methods of electronic structure theory, as the use of smaller basis for weak off-diagonal blocks reduces the computational costs of the calculations.

Within the framework of supersymmetric quantum mechanics method, we study by an algebraic method the arbitrary *l*-wave bound states of the Schrödinger equation for the hyperbolical molecular potential by a proper approximation to nonlinear centrifugal term. The explicitly analytical formula of energy levels is derived, and the corresponding bound state wave functions are presented. The function analysis method is used to rederive the same energy levels of the quantum system under consideration to check the validity of this algebraic method. In addition, it is shown from numerical results of energy levels that above certain *α* parameter depending on the choices of potential parameters *V*_{1} and *V*_{2} the hyperbolical molecular potential cannot trap a particle as it becomes weaker and the energy level starts to turn positive when the potential parameter *α* becomes larger. © 2014 Wiley Periodicals, Inc.

The hyperbolical potential, as one of the important molecular model potential, has been widely used to describe the vibrational spectra of the ammonia molecule. An algebraic method is applied to the study of the parameter dependence of arbitrary wave bound in the non-relativistic theory, and it is then employed to derive the analytical energy levels of the Schrödinger equation with the hyperbolical potential.

Bimolecular homolytic substitution (S* _{H}*2) reactions of the methyl radical with a series of three-membered ring compounds have been given a systematic theoretical study. These reactions proceed predominantly via the backside displacement. The formation of the new radical product is thermodynamically favorable probably due to the release of the ring strain. Natural bond orbital analysis reveals that SOMO σ*(C-X) (X= C, N, O) interaction plays a major role in these S

Bimolecular homolytic substitution (S* _{H}*2) reactions are regarded as one of the principle tools in synthetic chemistry. S

We discuss a method to follow step-by-step time evolution of atomic and molecular systems based on quantum electrodynamics. Our strategy includes expanding the electron field operator by localized wavepackets to define creation and annihilation operators and following the time evolution using the equations of motion of the field operator in the Heisenberg picture. We first derive a time evolution equation for the excitation operator, the product of two creation or annihilation operators, which is necessary for constructing operators of physical quantities such as the electronic charge density operator. We, then, describe our approximation methods to obtain time differential equations of the electronic density matrix, which is defined as the expectation value of the excitation operator. By solving the equations numerically, we show “electron-positron oscillations,” the fluctuations originated from virtual electron-positron pair creations and annihilations, appear in the charge density of a hydrogen atom and molecule. We also show that the period of the electron-positron oscillations becomes shorter by including the self-energy process, in which the electron emits a photon and then absorbs it again, and it can be interpreted as the increase in the electron mass due to the self-energy. © 2014 Wiley Periodicals, Inc.

When an electron moves, it creates an electromagnetic field around itself, and in turns this field has an effect on the electron. In quantum electrodynamics (QED), in which electromagnetic field is quantized to be photons, this so-called self-energy effect is viewed as the process in which the electron emits a photon and then absorbs it back. How to describe the self-energy effect in time-resolved QED simulations is the subject of this research.

We introduce a new type of spatially restricted basis function (zero beyond a characteristic *r*_{0} value of the radial coordinate) that makes it possible to obtain, in nonconfined systems, similar results to STO functions. This is important because the use of this kind of functions enables the exact application a sort of zero differential overlap approximation to calculate properties of large systems. Our functions are a modification of the BO-*x*Z box orbitals introduced by Lepetit et al. First, we replaced these orbitals by a function that is easier to obtain and generalize, that we named “simplified box orbital” (SBO), and we have shown some advantages of the SBO over BO and standard STO functions. Second, we obtained Gaussian developments for both the original BO orbitals and the new SBO orbitals. In this way, it becomes possible to manage our SBO orbitals with standard quantum chemistry software like GAUSSIAN or similar programs. © 2014 Wiley Periodicals, Inc.

A new type of spatially restricted basis functions is introduced. The new functions are easy to use, but the test accomplished with atomic and molecular calculations lead to results similar to those found by using standard Slater-type-orbital basis functions. In order to facilitate the use of the new functions with standard quantum chemical packages, gaussian developments “-*n*G” for new functions are supplied.

We have studied the CO oxidation over neutral, anionic, and cationic gold hexamer clusters using density functional theory which elucidates the effect of cluster charge state on the catalytic activity. Herein, we have considered the conventional bimolecular Langmuir–Hinshelwood mechanism with coadsorbed CO and O_{2} at the neighboring sites in all the clusters. Among the three clusters,
entails lower barriers during the various steps of the oxidation mechanism. The stability of all the species including the transition states with respect to the interacting species in
indicates no thermal activation. Our study suggests better catalytic activity of
as compared to the neutral and cationic counterparts. © 2014 Wiley Periodicals, Inc.

Small gold clusters exhibit excellent catalytic activity toward many important reactions. Gold hexamer is one such small cluster with the potential to act as a catalyst for reactions like CO oxidation. Density Functional Theory shows that neutral, anionic, and cationic Au_{6} clusters exhibit different activity toward CO oxidation. Anionic Au_{6} is the catalytically most active cluster and the proposed pathway for CO oxidation on
requires no thermal activation.

Based on the relation between quantum mechanical concepts such as effective Hamiltonians (EHs), perturbation theory (PT), and unitary transformations, and phenomenological aspects of spin Hamiltonians (SHs), the present tutorial tries to address the basics of the SH formalism. Using simple physical models and historical important examples, we have reviewed the derivation methods and applications of the SHs for a brief and in-depth description of various sources of anisotropies and interactions such as electronic (EZ), and nuclear Zeeman (NZ), terms, electron-exchange interaction (EE), zero-field splitting (ZFS), spin–spin (SS), spin-orbit (SO), nuclear quadrupole (NQ), and hyperfine couplings (HFCs), in a step-wise manner. In this way, this tutorial is tailored for the graduate students and young researchers who intend to begin their studies in the field of magnetism, electron magnetic resonance (EMR), spectroscopy, and related areas. © 2014 Wiley Periodicals, Inc.

Based on the relation between quantum mechanical concepts such as effective Hamiltonians, perturbation theory and unitary transformations, and phenomenological aspects of the spin Hamiltonians, this tutorial tries to address the basics of the spin Hamiltonian formalism.

With a view to understand the diffusion of radionuclides through the silicon carbide layers in tristructural isotropic coated fuel particles, density functional theory calculations are applied to assess the interaction of palladium, silver, tin, and caesium with silicon carbide. The silicon carbide molecule (Si_{2}C_{2}), crystalline cubic silicon carbide (β-SiC), and the (120) ∑5 grain boundary of β-SiC are investigated to elucidate the differences in the interactions of silicon carbide with these elements. The main stabilizing forces in the PdSi_{2}C_{2} complex were found to be donor-acceptor charge transfer (covalent) interactions, the Ag and Sn complexes involve significant contributions from both electrostatic and covalent interactions, while the Cs atom is bonded dominantly by electrostatic forces. For the unconstrained MSi_{2}C_{2} model, the following energetic ordering was obtained: Pd > Sn > Cs > Ag. The steric constraints in the bulk SiC and on the grain boundary change the order of binding energies to Pd > Ag > Sn > Cs in the interstitials and Pd > Sn > Ag > Cs in vacancies and at the grain boundary. By comparing the incorporation energies in the solid phases, it is possible to group these elements by similarities in the patterns of incorporation energies. Silver and palladium form a group with carbon, tin is grouped with silicon, and caesium is on its own. © 2014 European Commission. International Journal of Quantum Chemistry published by Wiley Periodicals, Inc.

The diffusion of radionuclides through the silicon carbide layers in tristructural isotropic coated fuel particles is an intriguing problem in nuclear industry. Density functional theory calculations on molecular and solid-state models provide insight into the nature of the interaction of palladium, silver, tin, and caesium with silicon carbide.

A set of atomic shell indicators is presented based on the idea to express the positive kinetic energy density with a density-based ansatz multiplied by a modifying function. It is shown that all modifying functions reveal the atomic shell structure and all but one may serve as chemical bonding descriptors. This study reveals that the real space description of the atomic shell structure is very robust with respect to the proposed ansatz since all derived indicators exhibit the atomic shell structure very close to the ideal one or do not reveal a shell structure at all. © 2014 Wiley Periodicals, Inc.

A set of atomic shell indicators is presented based on the idea to express the positive kinetic energy density with a density-based ansatz multiplied by a modifying function. The modifying functions reveal the shell structure and may serve as chemical bonding descriptors. The real space description of the shell structure is very robust with respect to the proposed ansatz since all derived indicators exhibit the atomic shell structure very close to the ideal one.

In this article, we prove some general theorems about representations of finite groups arising from the inner semidirect product of groups. We show how these results can be used for standard applications of group theory in quantum chemistry through the orthogonality relations for the characters of irreducible representations. In this context, conditions for transitions between energy levels, projection operators, and basis functions were determined. This approach applies to composite systems and it is illustrated by the dihedral group related to glycolate oxidase enzyme. © 2014 Wiley Periodicals, Inc.

Symmetries play a fundamental role in quantum chemistry. The rules of spectroscopy, for example, may be derived of the representation of finite groups. In this context, the concept of inner semidirect product can be explored, resulting in the conditions for transitions between energy levels, projection operators, and basis functions.

Quantum time-evolution equations for the density matrix are formulated in the unrestricted Hartree–Fock approximation, with an emphasis on the nonperturbative effect due to a sudden or gradual onset of a strong external field. Numerical simulations are performed for ideal Fermi gas around a square-well potential which is switched on dynamically. When the switching is fast enough, an oscillatory motion of the particle is induced by a nonadiabatic transition at the Landau–Zener crossing point, which is most clearly seen in a small-size system. When the switching is sufficiently slow, the simulation corroborates the adiabatic theorem. It is shown that the Anderson's infrared catastrophe in a metal is strongly enhanced by the nonperturbative effect. The Keldysh formula of atomic multiphoton ionization can also be derived from the nonperturbative term in the density-matrix equation, indicating a wide applicability of the present theory. © 2014 Wiley Periodicals, Inc.

When a strong, local attractive potential is switched on abruptly to a mesoscopic Fermi gas, the system is driven to a nonstationary state, giving rise to a quantum oscillation. This phenomenon has been demonstrated through the time evolution equations for the density matrix, which are applicable to a wide variety of quantum dynamics from nonadiabatic to adiabatic regime.

This study deals with a reinvestigation on the maximum oxidation state of gold. Density functional calculations are performed on geometries and stabilities of AuCl* _{n}* species for

The maximum oxidation state of gold (Au) with chlorine ligands is disputed. Quantum chemical calculations show Au that can bind successively up to six Cl atoms forming stable octahedral
complex. However, neutral AuCl_{6} exists in the form of (AuCl_{4})Cl_{2} complex, in which Cl_{2} moiety interacts weakly with the central gold atom. Thus, it can be concluded that the maximum oxidation state of Au does not exceed +5.

Accurate stereostructure of DNA in the nucleosomes has been established recently with the aid of more precise crystal structure investigations. Using this structure, Hartree–Fock crystal orbital calculations have been performed on the DNA parts of the nucleosomes. The obtained band structure was used to calculate the hole mobilities of the corresponding DNA parts. These results were used further to investigate the effect of Cl^{−} ions which enter in the cell nucleus through channels in the nuclear membrane. Our results show how Cl^{−} ions can weaken the DNA–protein interactions which can lead to the onset of cancer. Other molecules can also bind to DNA or photon can excite a nucleotide base in the stack. In both cases, a soliton can appear which causes long-range effect (disturbance of protein synthesis, double strand breaking). © 2014 Wiley Periodicals, Inc.

Large-scale quantum mechanical models can be successful applied to study the disturbances induced by the excess of ions, chemical carcinogens, or different radiation. The band structure model can properly describe the long-range propagation of the charge carriers or solitary waves along the DNA chain. Possible origins of disturbance of protein synthesis, double strand breaking, and for development of the precancerous state of the cell are discussed in this study.

In this study, the optimal synthetic route for 2,4,6-trinitro-1,3,5-triazine (TNTA) was investigated. The synthesis of TNTA was performed using cyanamide (H_{2}NCN) as a starting material. In the first stage, a radical addition reaction was used to generate melamine, which is the precursor of TNTA. In addition, a gaseous nitration reaction using nitrogen dioxide radicals (^{•}NO_{2}) as the nitration agent was used to gradually induce radical substitutions to convert dicyandiamide (H_{2}NCN)_{2} to melamine (H_{2}NCN)_{3}. Additional nitration steps lead to triaminocyanide and, ultimately, TNTA. In addition, nitryl cyanide (O_{2}NCN) was also tested as a starting material for radical addition to generate dinitryl cyanide (O_{2}NCN)_{2}, trinitryl cyanide (O_{2}NCN)_{3}, and, finally, TNTA. The activation energy barrier in each of the reaction steps as well as the various synthetic routes were compared to provide insight into the design of more feasible routes for the synthesis of TNTA. © 2014 Wiley Periodicals, Inc.

TNTA (2,4,6-trinitro-1,3,5-triazine) is a newly developed highly energetic explosive material. Theoretical calculations are used to understand and develop new, more streamlined synthesis routes to this material. Reactions involving radical species are included for the first time in this study.

Positron spectroscopy is a remarkable, important tool in the fields of materials science and medicine. On page 1146 (DOI: 10.1002/qua.24641), Yuki Oba and Masanori Tachikawa report that theoretical modeling aids the interpretation of positron experiments and can predict the positron binding to large biomolecules. In the case of aspartame, a molecular orbital exists around the region with high electron density, indicating that the long-range electrostatic interaction plays the most crucial role in positron binding.

Thermochemical quantities must be accompanied by uncertainties that unambiguously convey their believed accuracy, which combines the achieved precision and perceived trueness. Branko Rusic reports on page 1097 (DOI: 10.1002/qua.24605) that the uncertainties of electronic structure results can be quantified either by benchmarking (Type A) or estimation (Type B), and should adhere to the universally accepted standard in thermochemistry of expressing them as 95% confidence intervals. The ubiquitous Mean Absolute Deviation (MAD) severely underestimates the conventional uncertainty used in thermochemistry.

The accepted convention for expressing uncertainties of thermochemical quantities, followed by virtually all thermochemical tabulations, is to provide earnest estimates of 95% confidence intervals. Theoretical studies frequently ignore this convention, and, instead, provide the mean absolute deviation, which underestimates the recommended thermochemical uncertainty by a factor of 2.5–3.5 or even more, and thus may vitiate claims that “chemical accuracy” (ability to predict thermochemical quantities within ±1 kcal/mol) has been achieved. Furthermore, copropagating underestimated uncertainties for theoretical values with uncertainties found in thermochemical compilations produces invalid uncertainties for reaction enthalpies. Two groups of procedures for determining the accuracy of computed thermochemical quantities are outlined: one relying on estimates that are based on experience, the other on benchmarking. Benchmarking procedures require a source of thermochemical data that is as accurate and reliable as possible. The role of Active Thermochemical Tables in benchmarking state-of-the-art electronic structure methods is discussed. Published 2014. This article is a U.S. Government work and is in the public domain in the USA. International Journal of Quantum Chemistry published by Wiley Periodicals, Inc.

Mean absolute deviation, frequently used to assess the accuracy of theoretical methods, significantly underestimates the conventional thermochemical uncertainty, and thus produces a number of unintended consequences. Two groups of procedures for determining the accuracy of computed thermochemical quantities are outlined: one relying on estimates that are based on experience, the other on benchmarking. Benchmarking state-of-the-art theory requires a source of highly accurate thermochemical data, such as Active Thermochemical Tables.

This perspective gives a brief overview of recent developments within the polarizable embedding (PE) method — a multiscale approach developed over the last years. In particular, we are concerned with a recent coupling of the PE method to a multiconfiguration self-consistent field (MCSCF) code. Current applications and target systems are outlined, and methods to incorporate dynamical correlation are discussed. With respect to dynamical correlation, the focus is on perturbative treatments as well as a range-separated multiconfigurational hybrid between MCSCF and density functional theory (MC-srDFT). A short discussion of CAS active spaces is also given. A few sample results using a retinal chromophore surrounded by a protein environment illustrate both the importance of the choice of active space and the importance of dynamical correlation. © 2014 Wiley Periodicals, Inc.

The polarizable embedding (PE) method is a multiscale approach which focuses on molecular response properties and spectroscopic constants. Recently, the PE method has been coupled to a multiconfiguration self-consistent field (MCSCF) approach. This method, denoted PE-MCSCF, finds application in the calculations of photosensitive proteins and transition metal complexes.

In this review, we discuss the current status of analytic derivative theory in relativistic quantum chemistry. A brief overview of the basic theory for the available relativistic quantum chemical methods as well as the state-of-the-art development of their analytic energy derivatives is given. Among the various relativistic quantum chemical methods, cost-effective approaches based on spin separation and/or on the matrix representation of two-component theory have been proven particularly promising for the accurate and efficient treatment of relativistic effects in electron correlation calculations. We highlight analytic derivative techniques for these cost-effective relativistic quantum chemical approaches including direct perturbation theory, the spin-free Dirac-Coulomb approach, and the exact two-component theory in its one-electron variant. An outlook is given on future developments of analytic energy derivative techniques for relativistic quantum chemical methods, again with an emphasis on cost-effective schemes. © 2014 Wiley Periodicals, Inc.

The current status of analytic-derivative theory in relativistic quantum chemistry for the efficient calculation of properties (geometries, electrical properties, etc.) is reviewed with a special emphasis on cost-effective schemes such as direct perturbation theory, spin-free four-component approaches, and exact two-component (X2C) theory.

The p*K*_{a} values of several biologically important small molecules in aqueous solution, such as salicylic acid, histamine, and dopamine, were determined by density functional theory combined with the polarizable continuum model, which has been proposed for predicting p*K*_{a} values of nucleic acids and proteins. These molecules have plural protonation sites and the inherent p*K*_{a} determines which protons exist at a specific pH. Taking into account the ensemble average, and that the order of the deprotonation steps is specific among several possible pathways, it emerged that the calculated p*K*_{a} values mostly reproduced the experimental ones within an error of ± 1.0 p*K*_{a} units. © 2014 Wiley Periodicals, Inc.

The acid dissociation constant and its logarithm (p*K*_{a}) are often used to specify the position of protons in biomolecules. A novel scheme to compute p*K*_{a} values based on quantum chemical calculations combined with a polarizable continuum model is applied to several biologically important small molecules in aqueous solution such as salicylic acid, histamine, and dopamine. These molecules have plural protonation sites whose inherent p*K*_{a} determines which protons exist at a specific pH.

The present study is concerned with the theoretical study of possible molecular switch systems. The 7-hydroxyquinoline-8-carboxamide molecule and its single-, double-, and triple-substituted derivatives are investigated with the aim of revealing characteristic switch features. Molecular switches can be considered as composed of a frame and a crane component. According to a recent study, the 7-hydroxyquinoline double-ring system constitutes the frame moiety, while a carboxamide group at position 8 plays the role of the crane part (Csehi et al., Phys. Chem. Chem. Phys. 2013, 15, 18048). The effect of single 2-,4-,6-methyl, double 2,4-, 2,6-diamino, and triple 2,4,6-triamino substitutions to the molecular frame has been investigated using high level *ab initio* techniques. As a possible reaction mechanism, excited state intramolecular hydrogen transfer mediated by the frame-crane torsion has been considered. At the terminal structures of this pathway, second-order approximate coupled-cluster (CC2) quality vertical excitation energies and oscillator strengths have been calculated for the three lowest-lying singlet electronic excited states of all the studied systems. Single point calculations at selected geometries of the reaction path were carried out at the CC2 level as well, while conical intersections (CIs) between the ground and first excited states near perpendicular twisted geometries were optimized using the complete active space self-consistent field method. To confirm the presence of CIs, nonadiabatic coupling terms have been derived and applying the topological line integral technique, the topological (or Berry) phase has been calculated surrounding the point of CI. The results of this work clearly demonstrate the fulfillment of several molecular switch properties by the investigated quinoline derivatives. An extensive comparison between the different compounds is presented as well. © 2014 Wiley Periodicals, Inc.

7-Hydroxyquinoline derivatives are investigated as suitable molecular switches. To confirm the presence of conical intersections, nonadiabatic coupling terms must be derived and used in constructing the topological phase of the molecule. First-principle modeling can be also applied to understand the effect of various functional groups on the molecular switch properties of the core quinoline compound.

The feature of positron binding to aspartame molecule was analyzed using the *ab initio* multicomponent molecular orbital method. All nine stable conformers for aspartame molecule have positive positron affinity (the binding energy of a positron) values, which means that a positron can be attached to parent aspartame molecule. Analyzing the positronic orbitals of positronic aspartame conformers and the electrostatic potential maps of the corresponding parent molecules, we found that long-range electrostatic interaction is the most crucial role in positron binding to aspartame molecule. We theoretically confirmed the possibility of positron binding to the conformers of aspartame molecule with strong dipole moment. © 2014 Wiley Periodicals, Inc.

Positron spectroscopy is a remarkable, important tool in the fields of materials science and medicine. Theoretical modeling aids the interpretation of positron experiments and can predict positron binding to large biomolecules. In the case of aspartame, molecular orbital exists around the region with high electron density, which indicates that long-range electrostatic interaction plays the most crucial role in positron binding.

Many chemical reactions involve bond-dissociation. This is also true for reactions at solid surfaces, in which the dissociation step is often limiting but facilitated in comparison to gas-phase reaction channels. This work considers N_{2} dissociation. The molecule is strongly bound and stretched geometries are chosen. Heterogeneous catalysis by copper is simulated. It was investigated in our previous work as it is in many ways a prototype metal presenting a close-packed surface here. These nitrogen molecules are adsorbed on copper and fixed geometries on the dissociation reaction pathway for stretched N_{2} are given using density functional theory (DFT) calculations in a plane-wave basis. This dissociating molecule appears to be underbound using the *ab initio* Perdew, Burke, Ernzerhof (PBE) DFT functional but while this phenomenon accounts for a few percent at 5 Å, at 6 Å, PBE gives less than 30% of the binding energy. This indicates the onset of dissociation. The PBE wave-functions at these bond-lengths serve as trial input for Quantum Monte Carlo (QMC) simulations of the ground states to obtain highly accurate correlated results for the associated activation barriers indicating the catalytic effect on this dissociation. The geometries from this bond-stretching study mimic the transition state (TS). This procedure requires no search for the actual TS geometry. Finite-size effects and fixed-node error are possible limitations to accuracy of this type of QMC study. We are able to limit fixed-node error, using certain trial wave-functions. The finite-size effect is considerable, although comparing two adsorbed geometries cancels about 90% with respect to clean surfaces. Unfolding the cell to simulate a 9 k-point grid (rather than a single k-point) reduces the remainder by at least a factor 130 but relations for calibrating the remaining (2 mHa) error on converged grids are also used. The pseudopotential used to represent the atomic core of copper must also be determined carefully: we leave 11 active electrons but include the 3d shell in the pseudopotential. © 2014 Wiley Periodicals, Inc.

Quantum Monte Carlo (QMC) methods are used to show that stretched N_{2} is significantly under-bound in density functional estimates. The deficit compared to QMC energies is used to locate a bond-lengththat behaves like the dissociation transition state. This geometry is adsorbed on Cu(111) and a QMC simulation of the combined system gives an indication of the dissociation barrier and its lowering compared to the gas phase. N radicals are the product of both channels.