12 HSiP/HPSi Transition State Location

This example is concerned with locating the transition state in the HPSi, HSiP isomerisation process, and calculating the associated vibrational frequencies. We provide sample jobs using both numerical and analytical techniques in the transition state location and subsequent force constant evaluation. Note that the latter example is computationally the most efficient, and should certainly be adopted for small-medium sized molecules.

12.1 Numerical Force Constants

In the first step we perform an initial SCF for subsequent use in the saddle point calculation.

Closed shell SCF Job

          #!/bin/csh -f
          setenv ed2 /scr1/user/hpsimain
          setenv ed3 /scr1/user/hpsidump
          setenv ed7 /scr1/user/ed7
          /scr1/wab/GAMESS-UK/bin/gamess << EOF
          title
          psih saddle point
          zmat ang
          p
          x 1 1.0
          si 1 psi 2 90.0
          h 1 ph 2 90.0 3 hpsi
          variables
          psi 2.053 type 3
          ph  2.44  type 3
          hpsi  51.02 type 3
          end
          enter
          EOF

In the subsequent location of the transition state, note the use of TYPE 3 which causes the program to calculate the complete force constant matrix numerically before commencing the search for the saddle point, and the use of XTOL to provide more stringent optimisation criteria in view of the subsequent force constant evaluation. LOCK is used to retain the initial SCF configuration throughout the search.

Transition State Job

          #!/bin/csh -f
          setenv ed2 /scr1/user/hpsimain
          setenv ed3 /scr1/user/hpsidump
          setenv ed7 /scr1/user/ed7
          /scr1/wab/GAMESS-UK/bin/gamess << EOF
          restart new
          bypass
          title
          psih <-> hpsi saddle point
          zmat angs
          p
          x 1 1.0
          si 1 psi 2 90.0
          h 1 ph 2 90.0 3 hpsi
          variables
          psi 2.053 type 3
          ph  2.44  type 3
          hpsi  51.02 type 3
          end
          runtype saddle
          lock
          xtol 0.0005
          enter 2
          EOF

Finally we present the job for numerical evaluation of the force constants at the optimised geometry. Note the use of restart in requesting usage of the geometry from the Dumpfile, rather than from the data file.

Numerical Force Constant Job

          #!/bin/csh -f
          setenv ed2 /scr1/user/hpsimain
          setenv ed3 /scr1/user/hpsidump
          setenv ed7 /scr1/user/ed7
          /scr1/wab/GAMESS-UK/bin/gamess << EOF
          restart 
          title
          psih <-> hpsi saddle point numerical fcm
          zmat angs
          p
          x 1 1.0
          si 1 psi 2 90.0
          h 1 ph 2 90.0 3 hpsi
          variables
          psi 2.053 type 3
          ph  2.44  type 3
          hpsi  51.02 type 3
          end
          runtype force
          vectors 2
          lock
          enter 3
          EOF

12.2 Analytic Force Constants

In the first step we perform the computation of the trial hessian under RUNTYPE HESSIAN control for subsequent use in the saddle point calculation.

Computing the trial Hessian

          #!/bin/csh -f
          cd /scr1/user
          setenv ed2 hpsimain
          setenv ed3 hpsidump
          /scr1/wab/GAMESS-UK/bin/gamess << EOF
          title
          psih trial hessian / SCF 
          zmat ang
          p
          x 1 1.0
          si 1 psi 2 90.0
          h 1 ph 2 90.0 3 hpsi
          variables
          psi 2.053 
          ph  2.44  
          hpsi  51.02 
          end
          runtype hessian
          enter
          EOF

In the subsequent location of the transition state, note the use of the FCM keyword on the RUNTYPE data line to restore the trial hessian computed in the first job and the use of XTOL to provide more stringent optimisation criteria in view of the subsequent force constant evaluation. LOCK is used to retain the initial SCF configuration throughout the search.

Transition State Job

          #!/bin/csh -f
          cd /scr1/user
          setenv ed2 hpsimain
          setenv ed3 hpsidump
          /scr1/wab/GAMESS-UK/bin/gamess << EOF
          restart new
          title
          psih <-> hpsi saddle point location / using trial hessian
          zmat angs
          p
          x 1 1.0
          si 1 psi 2 90.0
          h 1 ph 2 90.0 3 hpsi
          variables
          psi 2.053
          ph  2.44  
          hpsi  51.02 
          end
          runtype saddle fcm
          xtol 0.0005
          vectors 1
          lock
          enter 2
          EOF

Finally we present the job for analytic computation of the force constants at the optimised geometry under control of runtype hessian. Note the use of restart in requesting usage of the geometry from the Dumpfile, rather than from the data file.

Analytic Force Constant Job

          #!/bin/csh -f
          cd /scr1/user
          setenv ed2 hpsimain
          setenv ed3 hpsidump
          /scr1/wab/GAMESS-UK/bin/gamess << EOF
          restart
          title
          psih <-> hpsi saddle point / force constants
          zmat angs
          p
          x 1 1.0
          si 1 psi 2 90.0
          h 1 ph 2 90.0 3 hpsi
          variables
          psi 2.053
          ph  2.44  
          hpsi  51.02 
          end
          runtype hessian
          vectors 2
          lock
          enter 2
          EOF