HBFF-SVD Force Field Treatment of Ni(II) Porphine: Important Long Range Cross Terms
2003; American Chemical Society; Volume: 107; Issue: 4 Linguagem: Inglês
10.1021/jp0218037
ISSN1520-5215
AutoresHui‐Hsu Gavin Tsai, M. Cather Simpson,
Tópico(s)Analytical Chemistry and Chromatography
ResumoA systematic exploration of the importance of cross terms in the Ni(II) porphine force field is reported. Several force fields of varying complexity were generated using a modification of the Hessian-biased singular value decomposition (HBFF-SVD) approach originally developed by Goddard et al. The X-ray crystal structure, a B3LYP/6-31G(d,p) Hessian matrix, and experimental vibrational frequencies were used. The diagonal-only force field is inadequate for reproducing experimental frequencies. As anticipated, inclusion of 1,2 and 1,3 cross terms significantly improves results (total rms error 14.6 cm-1; in-plane rms error = 12.0 cm-1). The longer range terms in a complete, in-plane, force field improve performance dramatically (in-plane rms error = 4.8 cm-1). A total of 83 long range interaction constants have values ≥10 kcal/(mol geom-unit), and 5 are greater than 20 kcal/(mol geom-unit). For example, 1,6- and 1,9-(Cα−Cm)−(Cα−Cm) stretch−stretch, 1,4-(Cα−N)−(Cα−Cm), and 1,4-(Cβ−Cβ)−(Cα−N−Cα) stretch−bend interactions are large and positive. Coupling in- and out-of-plane motions (TORX) enhances out-of-plane accuracy. Though isotopomer data were omitted from the optimization, the HBFF-SVD force fields reproduce these data with high fidelity. Finally, the HBFF-SVD force fields are compared in detail to previous normal-mode analysis and scaled quantum mechanics studies of Ni porphine.
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