Molcas Forum

ABQTrap

Member

Registered: 2023-03-19

Posts: 24

transition state OPT using FindTS converge to minimum structure

Dear all,
    I tried to located the transition state geometry by keywords "FindTS" and "TSConstraints" in &SLAPAF. however, the calculation converged to a minimum structure, not the transition state, please check the output and input below. So how can I locate the right transition state? Thanks a lot.

       +----------------------------------+----------------------------------+
       +    Cartesian Displacements       +    Gradient in internals         +
       +  Value      Threshold Converged? +  Value      Threshold Converged? +
 +-----+----------------------------------+----------------------------------+
 + RMS + 3.6610E-06  1.2000E-03     Yes   + 2.4571E-06  3.0000E-04     Yes   +
 +-----+----------------------------------+----------------------------------+
 + Max + 4.4220E-06  1.8000E-03     Yes   + 2.4571E-06  4.5000E-04     Yes   +
 +-----+----------------------------------+----------------------------------+
 
 Geometry is converged in   1 iterations to a Constrained Minimum Structure
 
 FindTS was requested, but the TS regime was not reached.
 The converged structure is probably not the desired TS.

&Gateway
Coord=$MOLCAS/TS-2.xyz
Basis=def-tzvp
Group=C1
>>> Do while
&SEWARD
&SCF; KSDFT=B3LYP
&SLAPAF 
FindTS
PRFC
TSConstraints
a = Angle H2 O1 H3
Value
a = 180.0 degree
End of TSConstraints
>>> EndDo

Ignacio

Administrator

From: Uppsala

Registered: 2015-11-03

Posts: 1,085

Re: transition state OPT using FindTS converge to minimum structure

Apparently your initial structure is already satisfying the constraints, or very close to (and otherwise minimized). The way FindTS works is by first moving "uphill" in the potential energy surface, towards the constrained structure, and eventually it should release the constraints once it finds a negative curvature. In your case it does not have the opportunity because it's already converged.

Try starting farther from the expected TS (e.g. from reactants or products), setting the constraints past the expected TS and/or reducing the maximum step size.

ABQTrap

Member

Registered: 2023-03-19

Posts: 24

Re: transition state OPT using FindTS converge to minimum structure

Apparently your initial structure is already satisfying the constraints, or very close to (and otherwise minimized). The way FindTS works is by first moving "uphill" in the potential energy surface, towards the constrained structure, and eventually it should release the constraints once it finds a negative curvature. In your case it does not have the opportunity because it's already converged.

Try starting farther from the expected TS (e.g. from reactants or products), setting the constraints past the expected TS and/or reducing the maximum step size.

Dear Ignacio, thank you for your help and sorry for my late reply. After several attampts, the saddle method plus bond soft constraints seemed to work. Thanks a lot.