Improving the efficiency and reliability of the divide-and-conquer approach to constructing the electronic density

An analysis of the errors introduced by a divide-and-conquer approach to constructing the electronic density is performed for a series of 6–31G∗∗ density functional calculations on polypeptides. It is shown that problems can arise whether a distance criterion or a topology criterion is used to define a subsystemʹs buffer space. Large buffer space cutoffs are required to achieve high accuracy. With long cutoffs, errors are dominated by losses in variational flexibility. With short cutoffs, errors are dominated by the subsystem orbitalsʹ failure to be orthogonal to the true global molecular orbitals. The varying importance of different types of basis functions is exploited to define a multiple buffer space cutoff approach that will improve the efficiency of divide-and-conquer calculations.