Q. Perturbation selection takes time and the job does not proceed.

 

A. For the system with large active space, perturbation selection usually takes much cpu time. It does not mean that the calculation is in trouble. For example, the calculation with the active space of 330 MOs takes about two weeks for selecting the S and R operators in the step "PRES" with Compaq XP1000 workstation. Better algorithm has been developed and will be published soon..