MECP Optimization using State-Specific CASSCF

[Meghna Manae]

Dear Molpro Users,

Minimum Energy Crossing Point (MECP) optimizations between two electronic states of different spin multiplicities can be performed using state-averaged CASSCF in Molpro with singlet-triplet state-averaged gradients (detailed how-to with example input in this manual link https://www.molpro.net/info/2015.1/doc/manual/node646.html).

Since the singlet and triplet states are uncoupled in the non-relativistic picture (and hence the non-adiabatic coupling calculation is skipped for MECP optimizations), is it possible to use state-specific gradients to optimize an MECP?

Warm regards,

Meghna

[Clayton Mulvihill]

Meghna,

I don't know if there is a way to do what you are saying in Molpro. 

As a totally separate idea, you could use the NST code written by Ahren Jasper. This Fortran code finds the MECP by calling either Molpro or Gaussian with whatever QC method you would like to use (and there is no state averaging of gradients). You can find the code at https://tcg.cse.anl.gov/papr/codes/mess.html, or you could also try the Auto-Mech GitHub repository (the latter is more up to date). 

Hope this helps!

-Clayton

[Meghna Manae]

Dear Clayton,

Thank you so much for the suggestion. Yes, coupling gradients calculated from Molpro with a seprarate optimizer would certainly solve my problem.

Warm regards,

Meghna

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