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Comparison of basis set effects and the performance of ab initio and DFT methods for probing equilibrium fluctuations

✍ Scribed by Ross C. Walker; Ian P. Mercer; Ian R. Gould; David R. Klug

Publisher: John Wiley and Sons
Year: 2006
Tongue: English
Weight: 727 KB
Volume: 28
Category: Article
ISSN: 0192-8651
DOI: 10.1002/jcc.20559

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✦ Synopsis

Abstract

The electronic absorption and emission spectra of large molecules reflect the extent and timescale of electron‐vibration coupling and therefore the extent and timescale of relaxation/reorganization in response to a perturbation. In this paper, we present a comparison of the calculated absorption and emission spectra of NADH in liver alcohol dehydrogenase (LADH), using quantum mechanical/molecular mechanical methods, in which we vary the QM component. Specifically, we have looked at the influence of basis set (STO‐3G, 3‐21G*, 6‐31G*, CC‐pVDZ, and 6‐311G**), as well as the influence of applying the DFT TD‐B3LYP and ab initio TD‐HF and CIS methods to the calculation of absorption/emission spectra and the reorganization energy (Stokes shift). The ab initio TD‐HF and CIS methods reproduce the experimentally determined Stokes shift and spectral profiles to a high level of agreement, while the TD‐B3LYP method significantly underestimates the Stokes shift, by 45%. We comment on the origin of this problem and suggest that ab initio methods may be naturally more suited to predicting molecular behavior away from equilibrium geometries. © 2006 Wiley Periodicals, Inc. J Comput Chem 28: 478–490, 2007

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