Molcas Forum

ethanthomas

Member

Registered: 2018-07-17

Posts: 4

Number of processors needed to compute numerical gradients efficiently

I just wanted to know how many processors can Molcas efficiently use when computing numerical gradients for a CASPT2 optimizations. Someone told me 4 but, why not 8?

valera

Administrator

Registered: 2015-11-03

Posts: 131

Re: Number of processors needed to compute numerical gradients efficiently

There is a fantastic rule, called Garbage Input -Garbage Output.
The correct answer depends on many factors about your run, which you didn't specify. In a simple way, the number of displacements in NG is the ideal number for MOLCAS_NPROCS. But you also should consider the fact that if these processes are not individual CPUs, but cores - you might hit a limit in I/O.