Automatic Determination of Buffer Region in Divide-anc-Conquer Quantum Chemical Calculations

A scheme to automatically determine the buffer region in the divide-and-conquer (DC) large-scale quantum chemi cal method is introduced. The buffer region directly relates to the error introduced by the DC method. In the iterative DC Hartree-Fock procedure, the automatic scheme adopts two-layered buffer region and gradually enlarges the buffer region by evaluating the energy contribution from the outer buffer region and determining whether the buffer region should be enlarged or not based on the energy-based threshold. On the other hand, in the non-iterative DC second-order Møller-Plesset perturbation calculation, the energy contribution is approximately estimated for the atoms in the buffer region and only those atoms that contribute more than an energy-based threshold are left in the buffer region. We demonstrated that both methods achieve almost constant accuracy in the energy using only one energy-based threshold as a parameter.