Less vir. orb. in CCSDT calculation with Molpro

Hello,

I need to calculate the CCSDT energies of a fairly large system in a completely uncontracted basis set and want to reduce my memory requirements by restricting the excitations to certain virtual orbital below a energy cutoff value of, say, 30 a.u. (which is e.g. possible in DIRAC). For my system I'm restricted to Molpro2015 and the implemented MRCC interface.

Let's say, the totally uncontracted basis set produces 500 virtual orbitals, but I want to kick out the upper 400 virtuals to speed up my calculation.

The only possibility I found for doing that is by manually modifying the vector in the fort.56 file and the orbitals and the corresponding integrals in the fort.55 file.

Is there possibly another way of doing this or a work-around?

Many thanks in advance!

Unfortunately, currently this is the only way.

Thank you, I will start scripting then.

It just came into my mind that there is a better option. You should try MP2 natural orbitals or optimized virtual orbitals (see the description of keyword ovirt in the manual as well as JCP 134, 124111, 2011). In this way your CCSDT energy will be more accurate, and you do not need to bother with the integral files.

Thank you, I'll give it a shot!

Follow-up question:

Is the program "ovirt" called automatically when "dmrcc" gets executed and the appropriate keyword is set? I'm using the MINP file format and cannot seem any difference between the two cases.

(Please see attached files)

Thanks again and best wishes,

Paul