Molcas Forum

serra_uam

Member

Registered: 2015-11-26

Posts: 1

IRC direction of the reaction vector

Hello everyone,

I would like to ask if there is an option to indicate how to follow a specific direction of the reaction path in an IRC calculation. And is there any keyword to restart the IRC calculation?

Thank you.

Last edited by serra_uam (2015-11-30 19:17:12)

Ignacio

Administrator

From: Uppsala

Registered: 2015-11-03

Posts: 1,012

Re: IRC direction of the reaction vector

Do you mean forward/backward, starting from a TS? With the "IRC" keyword, slapaf will run first the forward path, until a minimum or the specified number of points ("nIRC" keyword) is reached, then run the backward path. If you want the backward path being done first, the easiest is to supply the reaction vector manually ("REAC" keyword), and just change the sign of all components, so that backward means forward.

If you mean a MEP in mass-weighted coordinates, starting from a non-stationary point on the PES, it will be run following the gradient. You can specify (if I remember correctly) the initial direction with the "REAC" keyword as well, but after that the gradient at each point will be followed. If you don't specify "REAC" the gradient at the initial point will be followed too, which is usually what one wants.

And is there any keyword to restart the IRC calculation?

Not really, but you can continue the calculation if you re-use the WorkDir and don't run Gateway. Or simply run a MEP from your last available IRC point. It won't run the backward path after, though. For very long calculations/paths, you may want to run an IRC with a small number of points (say 10), and then continue the backward and forward paths with separate MEPs.

Last edited by Ignacio (2015-11-30 19:25:50)