Molcas Forum

debu_molcas

Member

Registered: 2016-11-13

Posts: 9

Second Order TS optimization

Dear all,
            Is it possible to optimize a second order transition state in MOLCAS? I have seen the keyword SADDle in the manual. In Page 199 it is described as "SADDle Step size reduction for each macro iteration of the saddle method" and in page 135 "SADDle SADDLE n Defines optimization onto an nth-order saddle point." Could you please explain why the keyword means different in different place?  From the second option I thought "SADDle=2" should be the keyword for second order TS optimization. So, I used the following input

>>>Do While

 &SEWARD
Title=Seward data
End of input

&RASSCF
Spin=1
Nactel=6 0 0
INACtive=18
Ras2 =6
End of input

 &ALASKA
 &SLAPAF
TS; PRFC
SADDLE
2

>>>EndDo

But Program says it is an unknown command.

Your help will be greatly appreciated. 

Thanks & Regards

Debasish

Ignacio

Administrator

From: Uppsala

Registered: 2015-11-03

Posts: 1,085

Re: Second Order TS optimization

The "Step size reduction" is a keyword for &GATEWAY (in combination with "RP-Coordinates"). The "n-th order saddle point" is a keyword for &CASVB, and it refers to the wavefunction optimization, not the geometry optimization. There is no "Saddle" keyword for &SLAPAF, which is why you get an error.

As far as I know, it's not possible to ask for a higher-order saddle point in a geometry optimization, but sometimes a regular TS optimization may converge to such a point.