Calculation of the IR spectrum of ethylbacteriochlorophyllide (A) by the density functional method

Abstract

The structure, the frequencies of the normal vibrations, and the absolute IR intensities of ethylbacteriochlorophyllide (A) are calculated in the approximation of the hybrid density functional B3LYP with the 6–31 G(d) basis set. The scaling of the quantum-mechanical force constants is performed by the Pulay method. The effective force field of ethylbacteriochlorophyllide (A) in the redundant and nonredundant coordinates is obtained. The vibrational IR spectrum is modeled. On the basis of the calculations performed, the experimentally determined IR spectrum of bacteriochlorophyll (A) is interpreted.