Journal of Physical Chemistry A, Vol.110, No.51, 13915-13922, 2006
Dual-basis analytic gradients. 1. Self-consistent field theory
Analytic gradients of dual-basis Hartree-Fock and density functional theory energies have been derived and implemented, which provide the opportunity for capturing large basis-set gradient effects at reduced cost. Suggested pairings for gradient calculations are 6-31G/6-31G**, dual[-f,-d]/cc-pVTZ, and 6-311G*/6-311++ G(3df, 3pd). Equilibrium geometries are produced within 0.0005 angstrom of large-basis results for the latter two pairings. Though a single, iterative SCF response equation must be solved ( unlike standard SCF gradients), it may be obtained in the smaller basis set, and integral screening further reduces the cost for well-chosen subsets. Total nuclear force calculations exhibit up to 75% savings, relative to large-basis calculations.