IRC from TS using CASSCF

[Siddharth Sankar Dutta]

Hi everyone,

I am trying to perform an IRC calculation at the CASSCF level in Molpro using the QSDPATH method, but I am encountering problems getting it to run successfully.

Could anyone provide an example input or guidance on how to perform IRC calculations for a CASSCF-optimized transition state in Molpro? Any suggestions regarding the correct workflow or common pitfalls would be greatly appreciated.

Thank you for your time and help.

Best regards,
Siddharth

[tibo...@gmail.com]

Dear  Siddharth,

To be completely honest I have never had much luck using Molpro's built-in IRC functionality, even for relatively simple reactions using MP2 or CCSD.

Therefore my recommendation is to use the open-source  geomeTRIC program maintained by Lee-Ping Wang, which can perform geometry optimization and IRC steps, and can use Molpro as the quantum chemistry engine.

Make sure to install the latest version of geomeTRIC, as the  geomeTRIC-Molpro interface has received some bugfixes.

CASSCF might bring substantial complications though, if there are orbitals leaving/entering the active space along the reaction path.

Best wishes

Tibor Győri