Run and restart an X2C calculation

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This examples shows how one can run a Hartree-Fock (HF) calculation in 2-component mode with the exact two component (X2C) Hamiltonian and restart a property calculation at the HF level in a second run without the need to re-do the X2C transformation.

The Br2 molecule (Br2.xyz) has linear symmetry (D_oo,h), and the program will detect this automatically. In most parts of the program the highest abelian subgroup (D2h) will be used instead of the full linear symmetry. In this example we use Dyall's augmented TZ basis dyall.av3z in uncontracted form.

The file (scf_x2c.inp) provides an input for the initial HF run. Prior to the HF the Hamiltonian transformation from 4- to 2-components will be performed and for restart purposes one should therefore save the files X2CMAT and AOMOMAT containing the Hamiltonian information and the file DFCOEF containing the (converged) MO-coefficients (keyword --outcmo below).

Run the first step in the example using:

pam --mol=Br2.xyz --inp=scf_x2c.inp --outcmo --get "X2CMAT AOMOMAT" 

Output will be written to the file scf_x2c_Br2.out, which can be monitored during the calculation.

scf_x2c.inp

**DIRAC
.WAVE FUNCTION
**MOLECULE
*BASIS
! Use the same basis for all atoms
.DEFAULT
dyall.av3z
**HAMILTONIAN
! Use the exact two-component Hamiltonian
! with atomic mean field spin-orbit
.X2C
**INTEGRALS
*READIN
! A limitation in the AMFI code requires an uncontracted basis
.UNCONTRACT
**WAVE FUNCTION
.SCF
*END OF

Br2.xyz

2
Br 0.0 0.0  1.244
Br 0.0 0.0 -1.244

In order to proceed in a second step with a property calculation of, e.g. the contact density at the Br nucleus, at the HF level, we consider the file (property_x2c.inp). Restarting from the (converged) MO-coefficients and reading the transformed X2C-Hamiltonian from file is done automatically once the file are present. We therefore restart the calculation using:

pam --mol=Br2.xyz --inp=property_x2c.inp --incmo --copy "X2CMAT AOMOMAT" 

Output will be written to the file property_x2c_Br2.out, which can be monitored during the calculation.

property_x2c.inp

**DIRAC
.PROPERTIES
**MOLECULE
*BASIS
! Use the same basis for all atoms
.DEFAULT
dyall.av3z
**HAMILTONIAN
! Use the exact two-component Hamiltonian
! with atomic mean field spin-orbit
.X2C
**INTEGRALS
*READIN
! A limitation in the AMFI code requires an uncontracted basis
.UNCONTRACT
**PROPERTIES
.RHONUC
*END OF