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Hongjiang Zhang - One of the best experts on this subject based on the ideXlab platform.
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Ability of a coupled electron Pair Approximation to treat single bond breakings
Chemical Physics Letters, 2010Co-Authors: Jean-paul Malrieu, Hongjiang ZhangAbstract:The self-consistent size-consistent CI ((SC)2CI), which considers all exclusion principle violating (EPV) diagrams, is able to treat single bond breakings, despite its single-reference character. It is shown here that a CEPA-3 (coupled electron Pair Approximation) dressing, considering only the EPVs through the occupied molecular orbitals, treats satisfactorily the single bond breaking processes, while the uniform dressings, e.g. CEPA-0, the averaged coupled Pair functional (ACPF) or averaged quadratic coupled cluster (AQCC) lead to non-convergence or spurious energy lowering in such processes. A number of test calculations illustrate this rationalizable feature.
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Ability of a coupled electron Pair Approximation to treat single bond breakings
Chemical Physics Letters, 2010Co-Authors: Jean-paul Malrieu, Hongjiang ZhangAbstract:International audienceThe self-consistent size-consistent CI ((SC)2CI), which considers all exclusion principle violating (EPV) diagrams, is able to treat single bond breakings, despite its single-reference character. It is shown here that a CEPA-3 (coupled electron Pair Approximation) dressing, considering only the EPVs through the occupied molecular orbitals, treats satisfactorily the single bond breaking processes, while the uniform dressings, e.g. CEPA-0, the averaged coupled Pair functional (ACPF) or averaged quadratic coupled cluster (AQCC) lead to non-convergence or spurious energy lowering in such processes. A number of test calculations illustrate this rationalizable feature
Gerrit C. Groenenboom - One of the best experts on this subject based on the ideXlab platform.
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size consistent multireference single and double excitation configuration interaction calculations the multireference coupled electron Pair Approximation
Journal of Chemical Physics, 1991Co-Authors: Pja Ruttink, J.h. Van Lenthe, R. Zwaans, Gerrit C. GroenenboomAbstract:A new size consistent extension to the multi reference configuration interaction method is described. The method termed multireference coupled electron Pair Approximation (MRCEPA) is akin to a multireference CEPA(0) approach, though nonlinear terms do receive separate attention. We show the performance of the approach in some model systems as well as in an application to calculation of ground and excited ππ* states of ethylene.
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Size consistent multireference single and double excitation configuration interaction calculations. The multireference coupled electron‐Pair Approximation
The Journal of Chemical Physics, 1991Co-Authors: Pja Ruttink, J.h. Van Lenthe, R. Zwaans, Gerrit C. GroenenboomAbstract:A new size consistent extension to the multi reference configuration interaction method is described. The method termed multireference coupled electron Pair Approximation (MRCEPA) is akin to a multireference CEPA(0) approach, though nonlinear terms do receive separate attention. We show the performance of the approach in some model systems as well as in an application to calculation of ground and excited ππ* states of ethylene.
Hiroshi Tatewaki - One of the best experts on this subject based on the ideXlab platform.
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effect of removing the no virtual Pair Approximation on the correlation energy of the he isoelectronic sequence ii point nuclear charge model
Journal of Chemical Physics, 2010Co-Authors: Yoshihiro Watanabe, Haruyuki Nakano, Hiroshi TatewakiAbstract:The correlation energies (CEs) of the He isoelectronic sequence Z=2–116 with a point nuclear charge model were investigated with the four component relativistic configuration interaction method. We obtained CEs with and without the virtual Pair Approximation which are close to the values from Pestka et al.’s Hylleraas-type configuration interaction calculation. We also found that the uniform charge and point charge models for the nucleus differ substantially for Z≥100.
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Effect of removing the no-virtual-Pair Approximation on the correlation energy of the He isoelectronic sequence.
The Journal of chemical physics, 2007Co-Authors: Yoshihiro Watanabe, Haruyuki Nakano, Hiroshi TatewakiAbstract:The correlation energies (CEs) for the He-like ions are studied with the virtual-Pair Approximation (VPA) and with the no-virtual-Pair Approximation (NVPA). In contrast to the nonrelativistic CEs, the CEs calculated with relativity fell sharply as the nuclear charge Z increased, although the CE calculated with the NVPA was considerably lower than with the VPA for the heavier atoms. It is shown that CE calculated with a Hylleraas-type function implicitly includes the effects of the excitations into negative-energy states, which corresponds to the VPA. The present results verify that the strong dependence on Z of the CE of He-like ions is an essential effect of the relativity.
B. Fultz - One of the best experts on this subject based on the ideXlab platform.
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Kinetics of short- and long-range B2 ordering in the Pair Approximation
Journal of Materials Research, 1990Co-Authors: B. FultzAbstract:The kinetic master equation is developed in the Pair Approximation to study disorder{r arrow}B2 order transformations in bcc binary alloys. Coupled sets of rate equations for the Pair variables are obtained for atom movements by either the direct interchange mechanism or the vacancy mechanism. Numerical integrations provide the nonequilibrium relaxations of short- and long-range order (SRO and LRO), and the vacancy balances between the two sublattices. For binary alloys, disorder{r arrow}order transformations were studied for all combinations of interatomic interaction strengths, activation barrier heights, and alloy stoichiometry variations. After a transient vacancy relaxation, all cases began with a quick relaxation of SRO, followed later and independently by the growth of LRO and additional SRO. There were some variations in kinetic path through SRO and LRO, moderate variations in overall kinetics, and large variations in vacancy balance. Some non-physical aspects of kinetics in the Pair Approximation are discussed.
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Kinetics of short- and long-range B2 ordering in the Pair Approximation
Journal of Materials Research, 1990Co-Authors: B. FultzAbstract:The kinetic master equation is developed in the Pair Approximation to study disorder ⇉ B2 order transformations in bee binary alloys. Coupled sets of rate equations for the Pair variables are obtained for atom movements by either the direct interchange mechanism or the vacancy mechanism. Numerical integrations provide the nonequilibrium relaxations of short- and long-range order (SRO and LRO) and the vacancy balances between the two sublattices. For binary alloys, disorder ⇉ order transformations were studied for all combinations of interatomic interaction strengths, activation barrier heights, and alloy stoichiometry variations. After a transient vacancy relaxation, all cases began with a quick relaxation of SRO, followed later and independently by the growth of LRO and additional SRO. There were some variations in kinetic path through SRO and LRO, moderate variations in overall kinetics, and large variations in vacancy balance. Some nonphysical aspects of kinetics in the Pair Approximation are discussed.
Jean-paul Malrieu - One of the best experts on this subject based on the ideXlab platform.
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Ability of a coupled electron Pair Approximation to treat single bond breakings
Chemical Physics Letters, 2010Co-Authors: Jean-paul Malrieu, Hongjiang ZhangAbstract:The self-consistent size-consistent CI ((SC)2CI), which considers all exclusion principle violating (EPV) diagrams, is able to treat single bond breakings, despite its single-reference character. It is shown here that a CEPA-3 (coupled electron Pair Approximation) dressing, considering only the EPVs through the occupied molecular orbitals, treats satisfactorily the single bond breaking processes, while the uniform dressings, e.g. CEPA-0, the averaged coupled Pair functional (ACPF) or averaged quadratic coupled cluster (AQCC) lead to non-convergence or spurious energy lowering in such processes. A number of test calculations illustrate this rationalizable feature.
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Ability of a coupled electron Pair Approximation to treat single bond breakings
Chemical Physics Letters, 2010Co-Authors: Jean-paul Malrieu, Hongjiang ZhangAbstract:International audienceThe self-consistent size-consistent CI ((SC)2CI), which considers all exclusion principle violating (EPV) diagrams, is able to treat single bond breakings, despite its single-reference character. It is shown here that a CEPA-3 (coupled electron Pair Approximation) dressing, considering only the EPVs through the occupied molecular orbitals, treats satisfactorily the single bond breaking processes, while the uniform dressings, e.g. CEPA-0, the averaged coupled Pair functional (ACPF) or averaged quadratic coupled cluster (AQCC) lead to non-convergence or spurious energy lowering in such processes. A number of test calculations illustrate this rationalizable feature
