TS Verification Workflows

Sella TS + Frequency Verification Workflow

Step 1 — TS Optimisation with Sella + DLC:

task: TS SELLA RHF STO-3G

GEOMETRY
  H  -1.200000   0.000000   0.000000
  H   0.000000   0.000000   0.000000
  H   1.200000   0.000000   0.000000
END

OPT
  Coord    dlc
  MaxCycle 150
END

Step 2 — Frequency Analysis on Converged TS Geometry:

task: FREQ RHF STO-3G

GEOMETRY
  # Paste the optimized TS geometry from step 1
  H  ...
  H  ...
  H  ...
END

Expected output for a genuine TS:

 Frequencies (cm⁻¹):  -1547.2   789.3   934.6

Step 3 (optional) — IRC from the TS:

task: RHF STO-3G

GEOMETRY
  # Same TS geometry
  H  ...
  H  ...
  H  ...
END

OPT
  IRC true
END

Basic TS Verification

Step 1 — TS Optimization (Berny):

task: TS RHF STO-3G

GEOMETRY
  O   0.000000   0.000000   0.000000
  H   1.100000   0.000000   0.500000
  H  -1.100000   0.000000   0.500000
END

OPT
  MaxCycle 100
END

Step 2 — Frequency Verification:

task: FREQ RHF STO-3G

GEOMETRY
  # Copy optimized TS geometry
  O  ...
  H  ...
  H  ...
END

A genuine TS shows exactly one imaginary frequency:

 Frequencies (cm⁻¹):  -1247.3   1652.1   3825.4

TS Verification with Hydrogen Transfer

Step 1 — TS Optimization with Sella + DLC:

task: TS SELLA RHF STO-3G

GEOMETRY
  H  -1.200000   0.000000   0.000000
  H   0.000000   0.000000   0.000000
  H   1.200000   0.000000   0.000000
END

OPT
  Coord    dlc
  MaxCycle 150
END