Electron Correlation in Molecules Using Direct Second Order MCSCF

1994 ◽  
pp. 179-206 ◽  
Author(s):  
Hans Jørgen Aagaard Jensen
Keyword(s):  
Electron Correlation ◽  
Second Order

Effect of angular electron correlation in He: Second-order calculations for transfer ionization

2008 ◽  
Vol 78 (1) ◽  
Author(s):  
A. L. Godunov ◽  
Colm T. Whelan ◽  
H. R. J. Walters
Keyword(s):  
Electron Correlation ◽  
Second Order ◽  
Transfer Ionization

Reexamination of the Symmetry Rule for Bond Distortions in Conjugated Hydrocarbons

2002 ◽  
Vol 2002 (8) ◽  
pp. 372-373
Author(s):  
Masahiro Kataoka
Keyword(s):  
Perturbation Method ◽  
Electron Correlation ◽  
Correlation Effect ◽  
Second Order ◽  
Order Perturbation ◽  
Mo Calculations ◽  
Geometrical Structures ◽  
Electron Correlation Effect ◽  
Conjugated Hydrocarbons

Pariser–Parr–Pople-type SCF MO calculations with the electron correlation effect given by the Brillouin-Wigner second-order perturbation method with Epstein–Nesbet energy denominators and by the Pople–Seeger–Krishnan correction show that the symmetry rule for bond distortions in conjugated hydrocarbons is effective for predicting the geometrical structures of [4 n+2]annulenes.

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.

Scaling in second order electron correlation calculations of potential energy curves and spectroscopic constants

1983 ◽  
Vol 50 (6) ◽  
pp. 1323-1333 ◽  
Author(s):  
Stephen Wilson ◽  
Vladimir Kellö ◽  
Jozef Noga ◽  
Miroslav Urban
Keyword(s):  
Potential Energy ◽  
Electron Correlation ◽  
Second Order ◽  
Potential Energy Curves ◽  
Spectroscopic Constants

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.

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