The Field-Adapted ADMA Approach: Introducing Point Charges

New developments of the adjustable density matrix assembler (ADMA) approach to macromolecular quantum chemistry are described, based on the original fuzzy density matrix fragmentation scheme combined with an approach of using point charges to approximate the effects of additional, distant parts of a given macromolecule in the quantum chemical calculation of each fragment. The ADMA approach divides a macromolecule (the target molecule) into fuzzy fragments, for which conventional quantum chemical calculations are performed using moderate-sized “parent molecules” which contain both the fragment and all the local interactions of the fuzzy fragment with its surroundings within a preselected distance. For any such distance criterion, that is, for any size limit for the parent molecules, the computational time scales linearly with the size of the macromolecule. As demonstrated in earlier papers, in the original, linear-scaling ADMA approach, the accuracy is fully controlled by this distance, and with a large en...