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 tha t problems can arise whether a distance criterion or a topology criter ion is used to define a subsystem's buffer space. Large buffer space c utoffs are required to achieve high accuracy. With long cutoffs, error s are dominated by losses in variational flexibility. With short cutof fs, errors are dominated by the subsystem orbitals' failure to be orth ogonal to the true global molecular orbitals. The varying importance o f different types of basis functions is exploited to define a multiple buffer space cutoff approach that will improve the efficiency of divi de-and-conquer calculations. (C) 1997 Published by Elsevier Science B. V.