The Experts below are selected from a list of 225 Experts worldwide ranked by ideXlab platform
Henry F Schaefer - One of the best experts on this subject based on the ideXlab platform.
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the treacherous potential Energy Hypersurface of agsio
Journal of Chemical Physics, 2003Co-Authors: K Balasubramanian, Henry F SchaeferAbstract:The AgSiO system has been a source of puzzlement for more than a decade, with experimental and theoretical studies providing bewildering conclusions regarding the structure of the molecule. State-of-the-art coupled cluster and multireference configuration interaction methods have been applied in the present work, in conjunction with techniques designed to incorporate relativistic effects. With the coupled cluster single and double excitation with perturbatively applied triples method [CCSD(T)], the Ag–SiO dissociation Energy is predicted to be 6.8 kcal/mole, with the equilibrium structure being a nearly isosceles triangle. However, a second minimum Ag–O–Si structure with bond angle ∼150° lies at less than 1 kcal/mole. With the multireference CI approach (up to 48 million configurations) the energetic order of these two minima is reversed. In contrast, both second-order perturbation theory and density functional theory predict an Ag–Si–O structure with bond angle ∼115° to be the global minimum. The present...
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the naphthylcarbene potential Energy Hypersurface
Journal of the American Chemical Society, 1997Co-Authors: Peter R Schreiner, Paul Von Ragué Schleyer, Henry F SchaeferAbstract:The naphthylcarbene potential Energy surface (PES) was examined ab initio, employing self-consistent field (SCF), second-order perturbation theory (MP2), and density functional (Becke3LYP) methods in conjunction with 6-31G*, DZ, DZP, and 6-311+G* basis sets. All stationary structures were characterized by vibrational frequency analyses at the Becke3LYP/6-31G* level; final energies were evaluated at the Becke3LYP/6-311+G*//Becke3LYP/6-31G* + ZPVE level. Cyclobuta[de]naphthalene is the global minimum on this part of the C11H8 PES. Generally, seven-membered benzocarbenes are no minima as they converge to their corresponding allenes. Both 1- and 2-naphthylcarbene have triplet ground states, but the small S−T gaps (ca. 5 kcal mol-1) allow facile rearrangements in the singlet manifold to take place. The triplet rotational barrier for the exo-methylene in 2-naphthylcarbene is relatively small (3.5 kcal mol-1) due to weak π-bonding. At low temperatures, singlet 2-naphthylcarbene equilibrates with 2,3-benzobicyclo...
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the gaoh hgao potential Energy Hypersurface and the necessity of correlating the 3d electrons
Journal of Chemical Physics, 1996Co-Authors: Claude A Richards, Yukio Yamaguchi, Henry F SchaeferAbstract: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) ...
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the nitrosyl azide potential Energy Hypersurface a high Energy density boom or bust
Journal of the American Chemical Society, 1996Co-Authors: John Morrison Galbraith, Henry F SchaeferAbstract:Motivated by the recent isolation and spectroscopic characterization of nitrosyl azide (N4O), we have undertaken an ab initio investigation of the originally reported structure as well as various structural isomers on the potential Energy Hypersurface. Geometries and harmonic vibrational frequencies have been predicted for the trans-chain isomer along with the 6 π electron potentially aromatic ring structure with various levels of theory up through the triple-ζ plus double polarization single and double excitation coupled cluster (TZ2P CCSD) method and the multireference configuration interaction method (MRCISD). In addition, estimates are made for extension to higher levels of theory, arriving at final predictions of re(ON1) = 1.176 A, re(N1N2) = 1.472 A, re(N2N3) = 1.272 A, re(N3N4) 1.423, ϑe(N1ON4) = 106.3° for the trans-chain and ring isomers, respectively. Energy relationships, b...
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the ethylenedione anion elucidation of the intricate potential Energy Hypersurface
Journal of Chemical Physics, 1995Co-Authors: Russell J Thomas, Bradley J Deleeuw, Paul Oleary, Brian J Duke, Henry F Schaefer, Brian OlearyAbstract:Ab initio molecular orbital theory has been used to study the controversial potential Energy surface of the ethylenedione anion C2O−2. Seven different basis sets, the largest being triple zeta plus two polarization functions and one set of higher angular momentum functions (TZ2Pf) in quality, were utilized in conjunction with five correlated methods, the highest‐level being coupled‐cluster theory including single, double, and perturbative triple excitations [CCSD(T)]. Equilibrium geometries and harmonic vibrational frequencies of the predicted 2Au trans‐bent ground state are presented. The Renner–Teller potential Energy surface resulting from the splitting of the doubly degenerate linear 2Πu transition state into the nondegenerate bent 2Au and linear 2Bu surfaces is also characterized by means of Energy predictions for these three states. Several recent peak assignments in the experimental spectrum, as well as the isotopic shifts associated with them, are supported by theory. A correct description of the ...
Dominique Dehareng - One of the best experts on this subject based on the ideXlab platform.
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critical points and reaction paths characterization on a potential Energy Hypersurface
Journal of Chemical Physics, 2000Co-Authors: Marienoelle Ramquet, Georges Dive, Dominique DeharengAbstract:Most of the time, the definitions of minima, saddle points or more generally order p (p=0,…,n) critical points, do not mention the possibility of having zero Hessian eigenvalues. This feature reflects some flatness of the potential Energy Hypersurface in a special eigendirection which is not often taken into account. Thus, the definitions of critical points are revisited in a more general framework within this context. The concepts of bifurcation points, branching points, and valley ridge inflection points are investigated. New definitions based on the mathematical formulation of the reaction path are given and some of their properties are outlined.
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Energy Hypersurface local properties of the o2hf 1 rearrangement
Chemical Physics Letters, 1992Co-Authors: Georges Dive, Dominique Dehareng, Patrick Culot, Jeanmarie GhuysenAbstract:Abstract This work analyses a case where Murrell's proposal, stating that a second-order point must lie above a first-order one, is apparently violated. Study at the SCF-UMP2 level within the D95 + + basis set, of one critical point of the O 2 HF − anion, previously proposed to be of order two by Lopez, shows the importance of the electronic correlation. The critical point associated with the 2 Π state should rather be considered as a superposition of two first-order ones. The present analysis reveals that this contradistinction can be explained by three unconsidered elements: the local symmetry, the electronic correlation and the internal variables description.
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Energy Hypersurface local properties of the O2HF−1 rearrangement
Chemical Physics Letters, 1992Co-Authors: Georges Dive, Dominique Dehareng, Patrick Culot, Jeanmarie GhuysenAbstract:Abstract This work analyses a case where Murrell's proposal, stating that a second-order point must lie above a first-order one, is apparently violated. Study at the SCF-UMP2 level within the D95 + + basis set, of one critical point of the O 2 HF − anion, previously proposed to be of order two by Lopez, shows the importance of the electronic correlation. The critical point associated with the 2 Π state should rather be considered as a superposition of two first-order ones. The present analysis reveals that this contradistinction can be explained by three unconsidered elements: the local symmetry, the electronic correlation and the internal variables description.
Georges Dive - One of the best experts on this subject based on the ideXlab platform.
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critical points and reaction paths characterization on a potential Energy Hypersurface
Journal of Chemical Physics, 2000Co-Authors: Marienoelle Ramquet, Georges Dive, Dominique DeharengAbstract:Most of the time, the definitions of minima, saddle points or more generally order p (p=0,…,n) critical points, do not mention the possibility of having zero Hessian eigenvalues. This feature reflects some flatness of the potential Energy Hypersurface in a special eigendirection which is not often taken into account. Thus, the definitions of critical points are revisited in a more general framework within this context. The concepts of bifurcation points, branching points, and valley ridge inflection points are investigated. New definitions based on the mathematical formulation of the reaction path are given and some of their properties are outlined.
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Energy Hypersurface local properties of the o2hf 1 rearrangement
Chemical Physics Letters, 1992Co-Authors: Georges Dive, Dominique Dehareng, Patrick Culot, Jeanmarie GhuysenAbstract:Abstract This work analyses a case where Murrell's proposal, stating that a second-order point must lie above a first-order one, is apparently violated. Study at the SCF-UMP2 level within the D95 + + basis set, of one critical point of the O 2 HF − anion, previously proposed to be of order two by Lopez, shows the importance of the electronic correlation. The critical point associated with the 2 Π state should rather be considered as a superposition of two first-order ones. The present analysis reveals that this contradistinction can be explained by three unconsidered elements: the local symmetry, the electronic correlation and the internal variables description.
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Energy Hypersurface local properties of the O2HF−1 rearrangement
Chemical Physics Letters, 1992Co-Authors: Georges Dive, Dominique Dehareng, Patrick Culot, Jeanmarie GhuysenAbstract:Abstract This work analyses a case where Murrell's proposal, stating that a second-order point must lie above a first-order one, is apparently violated. Study at the SCF-UMP2 level within the D95 + + basis set, of one critical point of the O 2 HF − anion, previously proposed to be of order two by Lopez, shows the importance of the electronic correlation. The critical point associated with the 2 Π state should rather be considered as a superposition of two first-order ones. The present analysis reveals that this contradistinction can be explained by three unconsidered elements: the local symmetry, the electronic correlation and the internal variables description.
Peter A Kollman - One of the best experts on this subject based on the ideXlab platform.
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walking on the free Energy Hypersurface of the 18 crown 6 ion system using free Energy derivatives
Journal of Chemical Physics, 1994Co-Authors: Piotr Cieplak, David A Pearlman, Peter A KollmanAbstract:Molecular dynamics simulations have been used to calculate free Energy derivatives with respect to nonbonded parameters for both ions and the host, 18‐crown‐6 in cation‐18‐crown‐6 complexes. The free Energy derivatives have been used to examine the free Energy Hypersurface for such complexes and to ‘‘predict’’ the optimal cationic ligand for 18‐crown‐6 complexation in aqueous solution. This method has promise to enable the refinement of the intermolecular interaction parameters for both hosts and guests in aqueous solution. In particular, we show that the optimal ion size for 18‐crown‐6 is calculated to be between the sizes of Na+ and K+, consistent with the experimental data. More generally, it has potential to be a powerful tool in computer aided molecular design.
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Walking on the free Energy Hypersurface of the 18‐crown‐6 ion system using free Energy derivatives
Journal of Chemical Physics, 1994Co-Authors: Piotr Cieplak, David A Pearlman, Peter A KollmanAbstract:Molecular dynamics simulations have been used to calculate free Energy derivatives with respect to nonbonded parameters for both ions and the host, 18‐crown‐6 in cation‐18‐crown‐6 complexes. The free Energy derivatives have been used to examine the free Energy Hypersurface for such complexes and to ‘‘predict’’ the optimal cationic ligand for 18‐crown‐6 complexation in aqueous solution. This method has promise to enable the refinement of the intermolecular interaction parameters for both hosts and guests in aqueous solution. In particular, we show that the optimal ion size for 18‐crown‐6 is calculated to be between the sizes of Na+ and K+, consistent with the experimental data. More generally, it has potential to be a powerful tool in computer aided molecular design.
Jeanmarie Ghuysen - One of the best experts on this subject based on the ideXlab platform.
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Energy Hypersurface local properties of the o2hf 1 rearrangement
Chemical Physics Letters, 1992Co-Authors: Georges Dive, Dominique Dehareng, Patrick Culot, Jeanmarie GhuysenAbstract:Abstract This work analyses a case where Murrell's proposal, stating that a second-order point must lie above a first-order one, is apparently violated. Study at the SCF-UMP2 level within the D95 + + basis set, of one critical point of the O 2 HF − anion, previously proposed to be of order two by Lopez, shows the importance of the electronic correlation. The critical point associated with the 2 Π state should rather be considered as a superposition of two first-order ones. The present analysis reveals that this contradistinction can be explained by three unconsidered elements: the local symmetry, the electronic correlation and the internal variables description.
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Energy Hypersurface local properties of the O2HF−1 rearrangement
Chemical Physics Letters, 1992Co-Authors: Georges Dive, Dominique Dehareng, Patrick Culot, Jeanmarie GhuysenAbstract:Abstract This work analyses a case where Murrell's proposal, stating that a second-order point must lie above a first-order one, is apparently violated. Study at the SCF-UMP2 level within the D95 + + basis set, of one critical point of the O 2 HF − anion, previously proposed to be of order two by Lopez, shows the importance of the electronic correlation. The critical point associated with the 2 Π state should rather be considered as a superposition of two first-order ones. The present analysis reveals that this contradistinction can be explained by three unconsidered elements: the local symmetry, the electronic correlation and the internal variables description.