Molcas Forum

Anugraha

Member

Registered: 2025-12-17

Posts: 22

Imposing Cs symmetry constraint in energy profile calculation

Dear All,
My molecule has Cs symmetry and i want to calculate energy profile along N-H stretching coordinate at the MS-CASPT2//SA2-CASSCF(8,8)/aug-cc-pVDZ level, while imposing the Cs symmetry constraint on the wavefunctions. I would appreciate an example of the input file format for this calculation. The molecule has a total of 72 electrons.

Ignacio

Administrator

From: Uppsala

Registered: 2015-11-03

Posts: 1,204

Re: Imposing Cs symmetry constraint in energy profile calculation

You may want to reconsider the use of symmetry. With symmetry you'll be forced to use numerical gradients, but without symmetry analytical gradients are available:

* This file could have been saved elsewhere
> file geom.xyz
4

N    -0.02309126    -0.00943438     0.00000000
H     0.35905589    -0.94190767     0.00000000
H     0.37178537     0.45144204     0.80448617
H     0.37178537     0.45144204    -0.80448617
> eof

> foreach R in (1.00, 1.01, 1.02, 1.03, 1.04, 1.05)

&GATEWAY
  Coord = geom.xyz
  Group = NoSym
  Basis = cc-pVDZ
  RICD
  Constraints
    d = bond N1 H2
   Values
    d = $R angstrom
  End of constraints

> do while

  &SEWARD

  &RASSCF
    NActEl    = 8
    Charge    = 0
    RAS2      = 7
    StAverage = 2
    RlxRoot   = 1

  &CASPT2
    Multistate = all
    IPEA       = 0.0

  &SLAPAF

> end do

* Save the converged geometry in a new file
> copy $Project.Opt.xyz $MOLCAS_OUTPUT/${Project}_$R.xyz
* And as input for the next scan point
> copy $Project.Opt.xyz geom.xyz

> end foreach

If you insist on using symmetry:

* This file could have been saved elsewhere
> file geom.xyz
4

N    -0.02309126    -0.00943438     0.00000000
H     0.35905589    -0.94190767     0.00000000
H     0.37178537     0.45144204     0.80448617
H     0.37178537     0.45144204    -0.80448617
> eof

> foreach R in (1.00, 1.01, 1.02, 1.03, 1.04, 1.05)

&GATEWAY
  Coord = geom.xyz
  Group = z
  Basis = cc-pVDZ
  RICD
  Constraints
    d = bond N1 H2
   Values
    d = $R angstrom
  End of constraints

> do while

  &SEWARD

  &RASSCF
    NActEl    = 8
    Inactive  = 1 0
    RAS2      = 5 2
    StAverage = 2
    RlxRoot   = 1

  &CASPT2
    Multistate = all
    IPEA       = 0.0

  &SLAPAF

> end do

* Save the converged geometry in a new file
> copy $Project.Opt.xyz $MOLCAS_OUTPUT/${Project}_$R.xyz
* And as input for the next scan point
> copy $Project.Opt.xyz geom.xyz

> end foreach

For comparison

R      NoSym                Cs
1.00  -56.383555700778324  -56.383555922730814
1.01  -56.383927277697623  -56.383927243585440
1.02  -56.384128639020759  -56.384128624844294
1.03  -56.384170556045497  -56.384170535410028
1.04  -56.384063259962922  -56.384063238865402
1.05  -56.383816445018773  -56.383816430207141
1.06  -56.383439305849919  -56.383439268545615

time   125 s                372 s

The larger the molecule, the more expensive numerical gradients will be.