SCF Accuracy Level

Jaguar can use integrals evaluated on a grid with the pseudospectral method, or fully analytic integrals. The grids used for various SCF iterations and the accuracy with which parts of the calculation are done greatly affect the timing, and sometimes the accuracy, of the entire calculation.

The default Quick setting1 Keyword iacc = 3 in the gen section. allows fast calculations to be performed, using several different pseudospectral grid types, and cutoffs that should generally produce well-converged energies. The Accurate setting,2 Keyword iacc = 2 in the gen section. which corresponds to tighter cutoffs (and therefore somewhat slower calculations), also uses a variety of pseudospectral grids. If you choose the Ultrafine setting,3 Keyword iacc = 1 in the gen section. the cutoffs are even tighter (very accurate), and only the ultrafine pseudospectral grid type is used. The Ultrafine setting may be helpful for cases with convergence or accuracy problems, but increases the computational cost by a factor of two to three. The remaining choice is Fully analytic,4 Keyword nops = 1 in the gen section. which turns off the pseudospectral method and uses the analytic methods for all integrals [183,184]. This choice is significantly slower than the pseudospectral method. However, it can be run in parallel with OpenMP threads—see Running a Multithreaded Jaguar Job with OpenMP.