RI-MP2 Gradient Calculation
of Large
Molecules Using the Fragment Molecular Orbital Method
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Abstract
The second-order Møller–Plesset perturbation
theory
(MP2) gradient using resolution of the identity approximation (RI-MP2
gradient) was combined with the fragment molecular orbital (FMO) method
to evaluate the gradient including electron correlation for large
molecules. In this study, we adopted a direct implementation of the
RI-MP2 gradient, in which a characteristic feature of the FMO scheme
was utilized. Test calculations with a small peptide presented a computational
advantage of the RI-MP2 gradient over the canonical MP2 gradient.
In addition, it was shown that the error of the RI-MP2 gradient, caused
by RI approximation, was negligible. As an illustrative example, we
performed gradient calculations for two biomoleculesa prion
protein with GN8 and a human immunodeficiency virus type 1 (HIV1)
protease with lopinavir (LPV). These calculations demonstrated that
the gradient including the correlation effect could be evaluated with
only about twice the computational effort of the Hartree–Fock
(HF) gradient