Contribution of triple substitutions to the electron correlation energy in fourth order perturbation theory

1980 ◽  
Vol 72 (7) ◽  
pp. 4244-4245 ◽  
Author(s):  
R. Krishnan ◽  
M. J. Frisch ◽  
J. A. Pople
Keyword(s):  
Perturbation Theory ◽  
Fourth Order ◽  
Electron Correlation ◽  
Correlation Energy ◽  
Order Perturbation ◽  
Order Perturbation Theory ◽  
Electron Correlation Energy

Analytic First-Order Derivatives of Partially Contracted N-Electron Valence State Second-Order Perturbation Theory (PC-NEVPT2)

2019 ◽  
Author(s):  
Yoshio Nishimoto
Keyword(s):  
Perturbation Theory ◽  
Electron Correlation ◽  
Valence State ◽  
Second Order ◽  
Order Perturbation ◽  
Order Perturbation Theory ◽  
Transition Energies ◽  
First Order ◽  
Static Electron ◽  
Second Order Perturbation Theory

A balanced treatment of dynamic and static electron correlation is important in computational chemistry, and multireference perturbation theory (MRPT) is able to do this at a reasonable computational cost. In this paper, analytic first-order derivatives, speci cally gradients and dipole moments, are developed for a particular MRPT method, state-specific partially contracted n-electron valence state second-order perturbation theory (PC-NEVPT2). Only one linear equation needs to be solved for the derivative calculation if the Z-vector method is employed, which facilitates the practical application of this approach. Comparison of the calculated results with experimental geometrical parameters of O<sub>3</sub> indicates excellent agreement, although the calculated results for O<sub>3</sub><sup>-</sup> are slightly outside the experimental error bars. The 0-0 transition energies of various methylpyrimidines and trans-polyacetylene are calculated by performing geometry optimizations and seminumerical second-order geometrical derivative calculations. In particular, the deviations of 0-0 transition energies of trans-polyacetylene from experimental values are consistently less than 0.1 eV with PC-NEVPT2, indicating the reliability of the method. These results demonstrate the importance of adding dynamic electron correlation on top of methods dominated by static electron correlation and of developing analytic derivatives for highly accurate methods.

A nondiagonal quasidegenerate fourth-order perturbation theory

1996 ◽  
Vol 20 (2) ◽  
pp. 351-364 ◽  
Author(s):  
Kathleen Kuhler ◽  
Mark R. Hoffmann
Keyword(s):  
Perturbation Theory ◽  
Fourth Order ◽  
Order Perturbation ◽  
Order Perturbation Theory

scholarly journals Locating Conical Intersections Using the Quasidegenerate Partially and Strongly Contracted NEVPT2 Methods

2020 ◽  
Author(s):  
Yoshio Nishimoto
Keyword(s):  
Perturbation Theory ◽  
Electron Correlation ◽  
Radiative Decay ◽  
Second Order ◽  
Decay Process ◽  
Order Perturbation ◽  
Order Perturbation Theory ◽  
Conical Intersections ◽  
Complete Active Space ◽  
Second Order Perturbation Theory

Conical intersections (CIs) play an important role in photochemistry because they sometimes govern the non-radiative decay process. However, accurate characterizations of CIs are not always straightforward. In this study, analytic gradients and interstate coupling vectors for the quasidegenerate partially and strongly contracted n-electron valence state second-order perturbation theory (QD-PC-NEVPT2 and QD-SC-NEVPT2) were developed and applied to locating CIs of benzene. The pilot application demonstrates that the results of both the methods are similar to the extended multistate complete active space second-order perturbation theory (XMS-CASPT2), while the lack of dynamic electron correlation resulted in a deviation of 0.7 eV.

scholarly journals Fourth Order Perturbation Theory for Normal Selfenergy in Repulsive Hubbard Model

2005 ◽  
Vol 74 (9) ◽  
pp. 2592-2597 ◽  
Author(s):  
Shogo Shinkai ◽  
Hiroaki Ikeda ◽  
Kosaku Yamada
Keyword(s):  
Perturbation Theory ◽  
Hubbard Model ◽  
Fourth Order ◽  
Order Perturbation ◽  
Order Perturbation Theory
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