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Ground and excited state CASPT 2 geometry optimizations of small organic molecules
Author(s) -
Page Christopher S.,
Olivucci Massimo
Publication year - 2003
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.10145
Subject(s) - ground state , excited state , small molecule , state (computer science) , chemistry , organic molecules , molecule , geometry , materials science , computer science , atomic physics , physics , organic chemistry , mathematics , algorithm , biochemistry
A method for computing second‐order multiconfigurational perturbation theory ( CASPT 2) energy gradients numerically has been implemented and applied to a range of elementary organic chromophores, including 1,3 butadiene, acrolein, and two protonated Schiff bases. Geometries of ground and excited states—as well as conical intersections—are compared with the corresponding CASSCF structures, illustrating the effect of including the correction for dynamical electron correlation. It is shown that the differences between the two methods are not readily categorized, but that, while individual changes in bond lengths can be quite large (∼0.01–0.02 Å), the natures and CASPT 2 energetics of the structures remain similar. Exceptions to this tend to be systems that have a strong ionic character and that are not well described at the CASSCF level. Basis set effects (double‐ vs. triple‐ζ) were examined for a limited number of examples, and found to be quite dramatic at both levels of theory. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 298–309, 2003