Generalized Valence Bond Theory Research Articles

Multiconfiguration Pair-Density Functional Theory for Transition Metal Silicide Bond Dissociation Energies, Bond Lengths, and State Orderings.

Transition metal silicides are promising materials for improved electronic devices, and this motivates achieving a better understanding of transition metal bonds to silicon. Here we model the ground and excited state bond dissociations of VSi, NbSi, and TaSi using a complete active space (CAS) wave function and a separated-pair (SP) wave function combined with two post-self-consistent field techniques: complete active space with perturbation theory at second order and multiconfiguration pair-density functional theory. The SP approximation is a multiconfiguration self-consistent field method with a selection of configurations based on generalized valence bond theory without the perfect pairing approximation. For both CAS and SP, the active-space composition corresponds to the nominal correlated-participating-orbital scheme. The ground state and low-lying excited states are explored to predict the state ordering for each molecule, and potential energy curves are calculated for the ground state to compare to experiment. The experimental bond dissociation energies of the three diatomic molecules are predicted with eight on-top pair-density functionals with a typical error of 0.2 eV for a CAS wave function and a typical error of 0.3 eV for the SP approximation. We also provide a survey of the accuracy achieved by the SP and extended separated-pair approximations for a broader set of 25 transition metal–ligand bond dissociation energies.

On the performance of generalized valence bond theory in predicting magnetic exchange coupling constant in organic diradicals: A comparison with Hartree-Fock theory

We have investigated four different already synthesized meta- and para-connected diradicals to get their magnetic exchange coupling constants (J) through generalized valence bond (GVB) approach and also with Hartree-Fock (HF) theory with a view to establish the superiority of GVB method over HF theory for the prediction of J. In doing so, at first optimization of these molecules are done at B3LYP level of density functional theory using the 6-31++g(d) basis set. With these optimized geometries, J values are computed at GVB method along with TZV basis set and these values are compared with those of the J values obtained using HF/TZV level of theory. Nonetheless, J values found in both the theoretical processes are also compared with the experimental findings. Thus, the supremacy of the wavefunction based GVB method in predicting J is established in comparison with the HF method.

Insights into the Electronic Structure of Ozone and Sulfur Dioxide from Generalized Valence Bond Theory: Addition of Hydrogen Atoms.

Ozone (O3) and sulfur dioxide (SO2) are valence isoelectronic species, yet their properties and reactivities differ dramatically. In particular, O3 is highly reactive, whereas SO2 is chemically relatively stable. In this paper, we investigate serial addition of hydrogen atoms to both the terminal atoms of O3 and SO2 and to the central atom of these species. It is well-known that the terminal atoms of O3 are much more amenable to bond formation than those of SO2. We show that the differences in the electronic structure of the π systems in the parent triatomic species account for the differences in the addition of hydrogen atoms to the terminal atoms of O3 and SO2. Further, we find that the π system in SO2, which is a recoupled pair bond dyad, facilitates the addition of hydrogen atoms to the sulfur atom, resulting in stable HSO2 and H2SO2 species.

Insights into the Electronic Structure of Molecules from Generalized Valence Bond Theory

In this article we describe the unique insights into the electronic structure of molecules provided by generalized valence bond (GVB) theory. We consider selected prototypical hydrocarbons as well as a number of hypervalent molecules and a set of first- and second-row valence isoelectronic species. The GVB wave function is obtained by variationally optimizing the orbitals and spin coupling in the valence bond wave function. The GVB wave function is a generalization of the Hartree-Fock (HF) wave function, lifting the double occupancy restriction on a subset of the HF orbitals as well as the associated orthogonality and spin coupling constraints. The GVB wave function includes a major fraction (if not all) of the nondynamical correlation energy of a molecule. Because of this, GVB theory properly describes bond formation and can answer one of the most compelling questions in chemistry: How are atoms changed by molecular formation? We show that GVB theory provides a unified description of the nature of the bonding in all of the above molecular species as well as contributing new insights into the well-known, but poorly understood, first-row anomaly.

Reply to “Comment on ‘Insights into the Electronic Structure of Ozone and Sulfur Dioxide from Generalized Valence Bond Theory: Bonding in O3 and SO2’”

ADVERTISEMENT RETURN TO ISSUEPREVCommentNEXTReply to “Comment on ‘Insights into the Electronic Structure of Ozone and Sulfur Dioxide from Generalized Valence Bond Theory: Bonding in O3 and SO2’”Thom H. Dunning, Jr.*, Tyler Y. Takeshita, and Beth A. LindquistView Author Information Department of Chemistry, University of Illinois at Urbana-Champaign, 601 S. Mathews Avenue, Urbana, Illinois 61801, United StatesCite this: J. Phys. Chem. A 2016, 120, 1, 171–172Publication Date (Web):December 14, 2015Publication History Received6 October 2015Revised7 December 2015Published online22 December 2015Published inissue 14 January 2016https://doi.org/10.1021/acs.jpca.5b09775Copyright © 2015 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views422Altmetric-Citations2LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (142 KB) Get e-AlertsSUBJECTS:Binding energy,Electronic structure,Molecules,Quantum mechanics,Wave function Get e-Alerts

Insights into the Electronic Structure of Ozone and Sulfur Dioxide from Generalized Valence Bond Theory: Bonding in O3 and SO2.

There are many well-known differences in the physical and chemical properties of ozone (O3) and sulfur dioxide (SO2). O3 has longer and weaker bonds than O2, whereas SO2 has shorter and stronger bonds than SO. The O-O2 bond is dramatically weaker than the O-SO bond, and the singlet-triplet gap in SO2 is more than double that in O3. In addition, O3 is a very reactive species, while SO2 is far less so. These disparities have been attributed to variations in the amount of diradical character in the two molecules. In this work, we use generalized valence bond (GVB) theory to characterize the electronic structure of ozone and sulfur dioxide, showing O3 does indeed possess significant diradical character, whereas SO2 is effectively a closed shell molecule. The GVB results provide critical insights into the genesis of the observed difference in these two isoelectronic species. SO2 possesses a recoupled pair bond dyad in the a"(π) system, resulting in SO double bonds. The π system of O3, on the other hand, has a lone pair on the central oxygen atom plus a pair of electrons in orbitals on the terminal oxygen atoms that give rise to a relatively weak π interaction.

Generalized valence bond description of chalcogen-nitrogen compounds. II. NO, F(NO), and H(NO).

The electronic structure of the ground state of NO and those of F(NO) and H(NO), that is, the XNO and NOX isomers with X = F, H, were analyzed within the framework of generalized valence bond theory. In distinct contrast to the ground state of NS, it was found that the two-center, three-electron π interaction in NO(X(2)Π) is composed of a lone pair on O and a singly occupied orbital on N. Thus, F and H addition to NO preferentially leads to FNO and HNO. Somewhat surprisingly, the NOF and NOH isomers were found to be weakly bound, although for different reasons. The NOF state has a very unusual through-pair interaction with a NO-F bond length 0.444 Å longer than its covalent counterpart in OF(X(2)Π), while NOH arises from the N((2)D) + OH(X(2)Π) separated atom limit, similar to what we found for NSH.

Generalized valence bond description of chalcogen-nitrogen compounds. I. NS, F(NS), and H(NS).

The electronic structures of the ground states (X(2)Π) of NS and those (X(1)A') of F(NS) and H(NS), where X(NS) collectively refers to the XNS and NSX isomers, were analyzed within the framework of generalized valence bond theory. The ground state of NS has a recoupled pair π bond, which has a profound effect on its reactivity. For example, the lowest-energy isomer of F(NS) is NSF, which has a recoupled pair bond dyad with N-SF and NS-F bonds lengths and strengths similar to their covalent counterparts in NS and SF. The ground state of NSH, on the other hand, is only weakly bound with a NS-H bond energy 40.20 kcal/mol smaller than that in SH and a N-SH bond energy 40.20 kcal/mol less than that in NS. At its equilibrium geometry, the NSH molecule is best viewed as derived from the N((2)D) + SH(X(2)Π) separated fragments, with the weak NS-H bond resulting from unfavorable interactions between the SH bond pair and the nitrogen lone pair. Addition of F/H atoms to the nitrogen atom in NS disrupts the NS recoupled pair bond, which weakens both the FN-S/HN-S and F-NS/H-NS bonds. In contrast to the formation of recoupled pair σ bonds, formation of the recoupled pair π bond in NS is expressed as a change in the spin-coupling coefficients, rather than an interchange of the orbitals.

Insights into the electronic structure of disulfur tetrafluoride isomers from generalized valence bond theory.

Sulfur and fluorine can participate in a variety of bonding motifs, lending significant diversity to their chemistry. Prior work has identified three distinct minima for disulfur tetrafluoride (S2F4) compounds: two FSSF3 isomers and one SSF4 species. We used a combination of sophisticated explicitly correlated coupled cluster calculations and generalized valence bond (GVB) theory to characterize the electronic structure of these species as well as additional stationary points on the potential energy surface with F2SSF2 connectivity. On the singlet surface, the two stationary points considered in this work with an F2SSF2 structure are first- or second-order saddle points and not minima. However, on the triplet surface, we discovered a novel C2 symmetric F2SSF2 minimum that was anticipated from the structure of an excited state ((3)B1) of SF2. Analysis using the GVB wave function in conjunction with the recoupled pair bonding model developed by our group provides a straightforward explanation of the bonding in all of the S2F4 structures considered here. In addition, the model predicted the existence of the F2SSF2((3)B) minimum.

New insights into the stability of alkenes and alkynes, fluoro-substituted or not: a DFT, G4, QTAIM and GVB study

Many undergraduate organic chemistry books do not agree with the order of relative stability of alkenes towards hydrogenation reactions. Although they ascribe the stability of alkenes to the number and spatial position of the alkyl groups attached to the vinyl carbon atoms, results from the quantum theory of atoms in molecules indicate that the influence of an alkyl substituent on the stability of unsaturated hydrocarbons arises from the slight removal of electron density of the π bond, not from donation of their charge density to unsaturated carbon atoms as stated in many text books. There is an inverse relation between delocalization index--the number of shared electrons between two atoms, or Wiberg bond index of C=C bond--and the number of methyl groups attached to the vinyl carbon atoms. Electron withdrawing groups (EWGs) attached to unsaturated carbon atoms of alkenes and alkynes have two different behaviors: slight EWGs (alkyl groups) stabilize unsaturated carbon atoms while the strong EWG destabilizes the unsaturated carbon atoms. Generalized valence bond theory was also used to study the ambiguous behavior of fluorine substituents bonded to vinyl carbon atoms.

QuanPol: A full spectrum and seamless QM/MM program

The quantum chemistry polarizable force field program (QuanPol) is implemented to perform combined quantum mechanical and molecular mechanical (QM/MM) calculations with induced dipole polarizable force fields and induced surface charge continuum solvation models. The QM methods include Hartree-Fock method, density functional theory method (DFT), generalized valence bond theory method, multiconfiguration self-consistent field method, Møller-Plesset perturbation theory method, and time-dependent DFT method. The induced dipoles of the MM atoms and the induced surface charges of the continuum solvation model are self-consistently and variationally determined together with the QM wavefunction. The MM force field methods can be user specified, or a standard force field such as MMFF94, Chemistry at Harvard Molecular Mechanics (CHARMM), Assisted Model Building with Energy Refinement (AMBER), and Optimized Potentials for Liquid Simulations-All Atom (OPLS-AA). Analytic gradients for all of these methods are implemented so geometry optimization and molecular dynamics (MD) simulation can be performed. MD free energy perturbation and umbrella sampling methods are also implemented.

An approximate diatomics in molecules formulation of generalized valence bond theory

The slow computational speed of the generalized valence bond perfect pairing method (GVB-PP) has been an impediment to its routine use. We have addressed this problem by employing a diatomics in molecules Hamiltonian derived from a second quantization perturbation approach. This results in all three- and four-centered two-electron integrals being dropped from the traditional GVB-PP calculation. For moderate sized molecules, as for example C20 computed with a double zeta + polarization basis, there is on average a fifty-fold decrease in computational times. In this article, we present the theory behind our approach and analyze the accuracy and speed of this approximate GVB-PP method for several cases where density functional methods have produced ambivalent results.

On the theoretical description of the chemisorption of the hydrogen atom on the metallic surface. Calculation of energy interaction of H with hcp Co and Ni surface clusters

A model, based on the generalized valence bond theory, capable of describing the interaction of hydrogen atom (H) with large molecular systems is proposed. The accuracy of the model has been checked by calculating the H 2 + and H 2 systems. Atomic spin densities for clusters having 1243 atoms have been obtained. The surface magnetic and chemisorption property differences between the Ni and Co metals have been analyzed. An extrapolation scheme suitable to obtain H chemisorption energies on infinite systems from the finite ones has been proposed. Size-converged results have been obtained for the Co. Potential energy surfaces of hydrogen, on and below, the Co surface have been provided.

Unrestricted Perfect Pairing: The Simplest Wave-Function-Based Model Chemistry beyond Mean Field

The perfect pairing (PP) approximation from generalized valence bond theory is formulated in an unrestricted fashion for both closed- and open-shell systems using a coupled cluster ansatz. In the model chemistry proposed here, active electron pairs are correlated, but the unpaired or radical electrons remain uncorrelated, leading to a linear number of decoupled cluster amplitudes which can be solved for analytically. The alpha and beta spatial orbitals are variationally optimized independently. This minimal treatment of electron-electron correlation noticeably improves upon symmetry-breaking problems and other pathologies in Hartree-Fock (HF) theory and may be computed using the resolution of the identity approximation at only a factor of several times more effort than HF itself. PP also generally predicts improved molecular structures over HF. This compact, correlated wave function potentially provides a useful starting point for dynamical correlation corrections.

Rule-Based Trial Wave Functions for Generalized Valence Bond Theory

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTRule-Based Trial Wave Functions for Generalized Valence Bond TheoryJean-Marc Langlois, Terumasa Yamasaki, Richard P. Muller, and William A. III GoddardCite this: J. Phys. Chem. 1994, 98, 51, 13498–13505Publication Date (Print):December 1, 1994Publication History Published online1 May 2002Published inissue 1 December 1994https://doi.org/10.1021/j100102a012RIGHTS & PERMISSIONSArticle Views267Altmetric-Citations17LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (885 KB) Get e-Alerts

Polyhedral hybrid approach to bonding in molecules containing transition metals

A polyhedral hybrid approach, based on generalized valence bond theory, is proposed to treat the electronic structure and bonding in transition metal molecules. A key feature of the approach is the ubiquity of “bent bonds” formed from overlapping hybrid orbitais.

Ordinary field‐theoretic methods for self‐consistent wave functions which describe bond formation and dissociation. II. Commutative coupling case

AbstractHartree–Bogoliubov–Valatin (HBV) theory may be implemented with Lipkin Hamiltonians to obtain self‐consistent BCS wave functions which describe bond formation and dissociation. These wave functions are in turn vacuua for Nambu's representation of Feynman–Dyson–Goldstone diagrammatic perturbation theory, and hence provide suitable references for the many‐body treatment of correlation. Exact SCF solutions of the HBV equations are equivalent to special even‐replacement MC–SCF solutions. The latter are similar to generalized valence bond theory, and require one Fock operator for each one‐particle shell. The commutative coupling case of HBV theory is realized when the number‐conserving renormalized one‐body and number‐nonconserving pairing operators commute. In this case, a set of orbital equations which involves a single Fock operator may be solved. Since this could prove to be a significant simplification for large systems, the commutative coupling and exact solutions are compared here for the fragmentation of H2 and F2. Results suggest that commutative coupling orbitals will be useful for the aforementioned many‐body theory.