Ground State Potential Energy Hypersurface Research Articles

A Spectroscopic and Computationally Minimal Approach to the Analysis of Charge-Transfer Processes in Conformationally Fluxional Mixed-Valence and Heterobimetallic Complexes.

Class II mixed-valence bimetallic complexes {[Cp'(PP)M]C≡C-C≡N[M'(PP)'Cp']}2+ (M, M'=Ru, Fe; PP=dppe, (PPh3 )2 ; Cp'=Cp*, Cp) exist as conformational ensembles in fluid solution, with a population of structures ranging from cis- to trans-like geometries. Each conformer gives rise to its own series of low-energy intervalence charge-transfer (IVCT) and local d-d transitions, which overlap in the NIR region, giving complex band envelopes in the NIR absorption spectrum, which prevent any meaningful attempt at analysis of the band shape. However, DFT and time-dependent (TD)DFT calculations with dispersion-corrected global-hybrid (BLYP35-D3) or local hybrid (lh-SsirPW92-D3) functionals on a small number of optimised structures chosen to sample the ground state potential energy hypersurfaces of each of these complexes has proven sufficient to explain the major features of the electronic spectra. Although modest in terms of computational expense, this approach provides a more accurate description of the underlying molecular electronic structure than would be possible through analysis of the IVCT band by using the static point-charge model of Marcus-Hush theory and derivatives, or TDDFT calculations from a single (global) minimum energy geometry.

Theoretical and experimental study of the OH radical reaction with HCN

The reaction rates of OH with H13CN and HC15N have been measured relative to that with H12C14N at 298 ± 2 K and 1013 ± 10 hPa in purified air by long-path FTIR spectroscopy; the 12C/13C and 14N/15N kinetic isotope effects were determined to be 0.9733 ± 0.0012 and 0.9840 ± 0.0016 (1σ), respectively. Ground-state potential energy hyper-surfaces of the reaction were investigated by quantum chemistry methods according to which the HCN + OH reaction proceeds via addition of OH to the carbon atom with a barrier height of 15.4 kJ mol−1. Master equation modelling of the reaction rate coefficient and kinetic isotope effects show good agreement with the experiments.

The π-type hydrogen bond with triple C–C bond acting as a proton-acceptor. A gradient-corrected hybrid HF-DFT and MP2 study of the phenol–acetylene dimer in the neutral S 0 ground state

The π-hydrogen bonded minimum on the S 0 ground state potential energy hypersurface (PES) of the neutral phenol–acetylene dimer is located and analyzed in details. Three DFT approaches – B3LYP, mPW1PW91, and PBE1PBE/6-31++G(d,p) along with the MP2/6-31++G(d,p) level of theory were used for the presented analyses. Both the standard and the counterpoise-corrected PESs of the studied dimer were explored. Besides the weak hydrogen-bonding interaction of a π-type, also purely electrostatic interaction of a dipole–quadrupole type between the monomeric units is responsible for the stabilization of this global minimum on the studied PESs. The computed counterpoise-corrected interaction and dissociation energies at all levels of theory are in excellent agreement with the estimations based on experimental spectroscopic data. Anharmonic OH stretching frequencies for the free phenol and the π-hydrogen-bonded phenol–acetylene complex were computed on the basis of 1D DFT and MP2 OH stretching potentials. While all DFT levels significantly overestimate the experimentally measured ν(OH) vibrational frequency shift, the corresponding MP2 value is in excellent agreement with the experimental data (70.2 vs. 68 cm −1). On the other hand, when the frequency shifts are computed within the harmonic approximation, all DFT levels are in fortuitous good agreement with the experiment, due to cancellation of errors. Passing to the counterpoise-corrected PESs has a little influence on the calculated harmonic and anharmonic vibrational frequency shifts of the phenol OH stretching mode. According to the charge-field perturbation analyses of the 1D OH stretching potentials, the purely electrostatic interaction of phenol with the proton-accepting acetylene molecule governs only a small portion of the overall OH vibrational frequency shift, while the role of electrostatics with this respect is more important at MP2 level of theory. However, all levels of theory lead to a conclusion that the dynamical changes of charge-transfer interaction in the course of OH stretching are the main factor governing the IR intensity enhancement of this vibrational transition upon π-hydrogen bonding, while the electrostatic interaction is of a second-order importance with respect to this. According to the second-order perturbation theory analysis of the Fock matrix (or its Kohn–Sham analog) within the NBO basis and the NBO deletion analyses, the charge-transfer between the monomeric units within the dimer is essentially one-directional (occurring from acetylene to phenol), and predominantly of a π → σ* type. The energetic effect of this interaction was estimated as well. The existence of another, much less stable minimum on the explored PESs, predicted on the basis of mainly electrostatic arguments, was also confirmed.

The GaOH–HGaO potential energy hypersurface and the necessity of correlating the 3d electrons

The ground state potential energy hypersurface of the GaOH–HGaO system has been investigated using high level ab initio molecular electronic structure theory. The geometries and physical properties of two equilibrium structures, one isomerization transition state and one inversion transition state were determined at the self-consistent field (SCF), configuration interaction with single and double excitations (CISD), coupled cluster with single and double excitations (CCSD), and CCSD with perturbative triple excitations [CCSD(T)] levels of theory with four sets of basis functions. It has been found that freezing the 3d electrons of the Ga atom in the correlation procedures is not appropriate for this system. For the energy difference ΔE (GaOH–HGaO) the freezing of the 3d electrons results in an error of 25 kcal/mol! The dipole moments, harmonic vibrational frequencies, and infrared (IR) intensities are predicted for the four stationary points. At the highest level of theory employed in this study, CCSD(T) using triple zeta plus double polarization with higher angular momentum and diffuse functions [TZ2P(f,d)+diff] basis set, the bent GaOH was found to be 41.9 kcal/mol more stable than the linear HGaO species; with the zero-point vibrational energy (ZPVE) correction, the energy separation becomes 40.4 kcal/mol. The classical barrier height for the exothermic isomerization (1,2 hydrogen shift) reaction HGaO→GaOH is determined to be 44.5 kcal/mol and the barrier height with the ZPVE correction 42.3 kcal/mol. The classical barrier to linearity for the bent GaOH molecule is determined to be 1.7 kcal/mol and the barrier height with the ZPVE correction to be 1.2 kcal/mol. The predicted dipole moments of GaOH and HGaO are 1.41 and 4.45 Debye, respectively. The effects of electron correlation reduce the dipole moment of HGaO by the sizable amount of 1.2 Debye. The two equilibrium species may be suitable for microwave spectroscopic investigation. Furthermore, they may also be detectable by IR techniques due to the relatively large intensities of their vibrational modes. The geometrical and energetic features are compared with those of the valence isoelectronic HXO–XOH systems, where X is a group IIIA atom and the HXO+–XOH+ systems, where X is a group IVA atom.

The GeOH+–HGeO+ system: A detailed quantum mechanical study

The ground state potential energy hypersurface of the GeOH+–HGeO+ system has been investigated employing ab initio electronic structure theory. First, geometries of two equilibrium and isomerization (1,2 hydrogen shift) reaction transition state were determined at the self-consistent-field (SCF), configuration interaction with single and double excitations (CISD), coupled cluster with single and double excitations (CCSD), and CCSD with perturbative triple excitations [CCSD(T)] levels of theory using four basis sets. A qualitatively incorrect geometry is predicted for GeOH+ unless f functions are included in the basis set. Second, physical properties including dipole moments, harmonic vibrational frequencies, and infrared (IR) intensities of three stationary points were evaluated at the optimized geometries. The effects of electron correlation reduce the dipole moment of HGeO+ by 1.25 Debye. At the highest level of theory employed in this study, CCSD(T) using the triple zeta plus double polarization with diffuse and higher angular momentum functions [TZ2P(f,d)+diff] basis set, linear GeOH+ is predicted to be more stable than linear HGeO+ by 71.7 kcal/mol. After correction for zero-point vibrational energies (ZPVEs), this energy difference becomes 70.3 kcal/mol. With the same method the classical barrier height for the exothermic isomerization (1,2 hydrogen shift) reaction HGeO+→GeOH+ is determined to be 30.3 kcal/mol and the activation energy (with the ZPVE correction) is 28.0 kcal/mol. The predicted dipole moments of GeOH+ and HGeO+ are 0.61 and 4.64 Debye, respectively. Thus, the HGeO+ ion may be suitable for a microwave spectroscopic investigation. On the other hand, the GeOH+ ion may be suitable for an IR spectroscopic study due to the strong IR intensities of the three vibrational modes. The geometrical and energetic features are compared with those of the valence isoelectronic HCO+–COH+ and SiOH+–HSiO+ systems.

The SiOH+–HSiO+ system: A high level ab initio quantum mechanical study

Ab initio electronic structure theory has been employed in order to investigate the ground state potential energy hypersurface of the SiOH+–HSiO+ system. Geometries and physical properties including dipole moments, harmonic vibrational frequencies, and infrared intensities of two equilibrium and isomerization (1,2 hydrogen shift) reaction transition state were determined. The self-consistent-field, configuration interaction with single and double excitations, coupled cluster with single and double excitations (CCSD), and CCSD with perturbative triple excitations [CCSD(T)] levels of theory were used with five basis sets. At the highest level of theory employed in this study, CCSD(T) using the triple zeta plus double polarization with diffuse and higher angular momentum functions basis set, linear SiOH+ is predicted to be more stable than linear HSiO+ by 66.1 kcal/mol. This energy difference becomes 64.1 kcal/mol with an appropriate zero-point vibrational energy (ZPVE) correction. At the same level of theory, the classical barrier height for the exothermic isomerization (1,2 hydrogen shift) reaction HSiO+→SiOH+ is determined to be 29.3 kcal/mol and the activation energy (with the ZPVE correction) is 27.3 kcal/mol. The geometrical and energetic features are compared with those of the valence isoelectronic HBO–BOH, HCO+–COH+, and AlOH–HAlO systems.

An ab initio study on the ground state HBO–BOH system

Ab initio electronic structure theory has been employed in order to investigate the ground state potential energy hypersurfaces of the HBO–BOH system. Geometries, dipole moments, harmonic vibrational frequencies, and infrared intensities of two equilibrium and two transition state [inversion (bending through linear geometry) and isomerization] structures were determined at the self-consistent-field (SCF), configuration interaction with single and double excitations (CISD), coupled cluster with single and double excitations (CCSD), and CCSD with perturbative triple excitations [CCSD(T)] levels of theory using three basis sets. The theoretically predicted geometries and physical properties agree very well with available experimental values. At the highest level of theory employed in this study, CCSD(T) using triple zeta plus double polarization with higher angular momentum function [TZ2P(f,d)] basis set, the linear HBO molecule is predicted to be 45.0 kcal/mol more stable relative to the bent BOH species; with the zero-point vibrational energy (ZPVE) correction this energy separation becomes 44.4 kcal/mol; the classical barrier height for the inversion motion of the bent BOH molecule is predicted to be 3.5 kcal/mol and the barrier height with the ZPVE correction is 3.0 kcal/mol; the classical activation energy for the isomerization (1,2 hydrogen shift) reaction BOH→HBO is determined to be 29.4 kcal/mol and the activation energy with the ZPVE correction is 26.6 kcal/mol.

High level ab initio study on the ground state potential energy hypersurface of the HCO+–COH+ system

The ground state potential energy hypersurface of the HCO+–COH+ system has been reinvestigated systematically using high level ab initio electronic structure theory. The geometries and physical properties of the two equilibrium and one isomerization transition state structures were determined at the self-consistent-field (SCF), configuration interaction with single and double excitations (CISD), coupled cluster with single and double excitations (CCSD), and CCSD with perturbative triple excitations [CCSD(T)] levels of theory with nine basis sets. First, the optimized geometries of the three stationary points at twenty eight (28) levels of theory were discussed. Second, the characteristics and responses of the molecular orbitals (MOs) with respect to the normal coordinates have been elucidated via energy derivative analysis technique. Third, dipole moments, harmonic vibrational frequencies, and infrared (IR) intensities were described. Finally, the relative energies among the stationary points have been compared. At the highest level of theory, CCSD(T) using triple zeta plus double polarization with diffuse and higher angular momentum functions [TZ2P(f,d)+diff] basis set, the linear HCO+ molecule is found to be 39.7 kcal/mol [37.7 kcal/mol with zero-point vibrational energy (ZPVE) correction] lower in energy relative to the linear COH+ molecule. At the same level of theory the activation energy for the isomerization reaction HCO+→COH+ is predicted to be 76.9 kcal/mol (72.6 kcal/mol with the ZPVE correction). Once the COH+ species is formed, therefore, it should be reasonably stable with respect to the isomerization reaction at low temperatures.

Canonical orbital energy derivative studies of the C 2H 2 and H 2CO ground state potential energy hypersurfaces

A study of first and second derivatives of the canonical orbital energies for the closed-shell self-consistent-field (SCF) wavefunction has been extended to tetratomic molecular systems. The first derivatives of the orbital energies in terms of the Cartesian coordinate were determined analytically and the second derivatives via the finite difference method, while the first and second derivatives of the electronic, nuclear and total energies were obtained analytically. At the stationary points these energy derivatives were uniquely transformed from the Cartesian to the normal coordinate system. Using the four equilibrium and three transition state structures of the closed-shell C 2H 2, : CCH 2, H 2CO and trans-HCOH molecules as examples, it is demonstrated that the derivatives of the energies with respect to the normal coordinates provide useful chemical information concerning the molecular structures and reactivities. The orbital energy derivative method may be used as a powerful semi-quantitative model in understanding and interpreting various chemical phenomena.

Open-chain and cyclic protonated ozone: the ground-state potential-energy hypersurface

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTOpen-chain and cyclic protonated ozone: the ground-state potential-energy hypersurfaceCynthia Meredith, Geoffrey E. Quelch, and Henry F. Schaefer IIICite this: J. Am. Chem. Soc. 1991, 113, 4, 1186–1193Publication Date (Print):February 1, 1991Publication History Published online1 May 2002Published inissue 1 February 1991https://doi.org/10.1021/ja00004a019RIGHTS & PERMISSIONSArticle Views95Altmetric-Citations33LEARN 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 (958 KB) Get e-Alerts Get e-Alerts

Studies of Reaction Mechanisms with All-valence Electron Semi-empirical SCF MO Theories. IX. The Role of Tetracyclo[4.2.0.02,805,7]oct-3-ene on the Ground State Potential Energy Hypersurfaces of (CH)8 Isomers

Abstract Tetracyclo[4.2.0.02,805,7]oct-3-ene (1) is estimated by a MINDO MO calculation to be moderately strained. Interaction between the ethylenic π orbital and the Walsh orbitals of the two cyclopropane rings is extensive in the ground state structure of 1. The third highest occupied MO is an out-of-phase combination of the ethylenic 2pπ AO’s on C3 and C4, while the corresponding in-phase combination appears in the lower unoccupied MO’s. The interconversion between 1 and bicyclo[4.2.0]octa-2,4,7-triene (2) is a typical symmetryallowed reaction as revealed by a smooth change in bond indices along the reaction coordinates. The isomerization of substituted cyclooctatetraenes via 1 and 2 (Eq. (2)) is predicted to be possible at elevated temperatures. The symmetry-allowed degenerate valence isomerization of 1 (Eq. (3)) is energetically less favorable due to skeletal constraint.