METHODS FOR PARALLEL COMPUTATION OF SCF NMR CHEMICAL-SHIFTS BY GIAO METHOD - EFFICIENT INTEGRAL CALCULATION, MULTI-FOCK ALGORITHM, AND PSEUDODIAGONALIZATION

We implemented our gauge-including atomic orbital (GIAO) NMR chemical shielding program on a workstation cluster, using the parallel virtual machine (PVM) message-passing system. On a modest number of nodes, we achieved close to Linear speedup. This program is characterized by se veral novel features. It uses the new integral program of Wolinski tha t calculates integrals in vectorized batches, increases efficiency, an d simplifies parallelization. The self-consistent field (SCF) step inc ludes a multi-Fock algorithm, i.e., the simultaneous calculation of se veral Fock matrices with the same integral set, increasing the efficie ncy of the direct SCF procedure. The SCF diagonalization step, which i s difficult to parallelize, has been replaced by pseudo-diagonalizatio n. The latter, widely used in semiempirical programs, becomes importan t in ab initio type calculations above a certain size, because the ult imate scaling of the diagonalization step is steeper than that of inte gral computation. Examples of the calculation of the NMR shieldings in large systems at the SCF level are shown. Parallelization of the dens ity functional code is underway. (C) 1997 by John Wiley & Sons, Inc.