Tutorial:Getting started DIRAC11

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Contents 1 References

DIRAC uses two files as inputs: the input file *.inp, which determines what should be calculated, and either a geometry file *.xyz, that provides the nuclear coordinates, or a molecule file *.mol, which defines the molecular geometry and also the basis set. These files are described in detail in the Manual. When DIRAC runs it writes its output to a text file, named after the molecule and input file names. If this file already exists, for example from a previous calculation, the old file is renamed to make place for the new output. The pam python script that launches the main DIRAC executable also writes some general information to standard output.

Let's try it out and run our first DIRAC calculation with the following minimal input (hf.inp) to calculate the Dirac-Coulomb Hartree-Fock ground state (with the default simple Coulombic correction (LVCORR) to approximate the contribution from SS|SS integrals ^[1]. ):

**DIRAC
.WAVE FUNCTION
**WAVE FUNCTION
.SCF
**MOLECULE
*BASIS
.DEFAULT
cc-pVDZ
*END OF INPUT

together with the following example geometry file (methanol.xyz):

6
Methanol. This is a comment line.
C       0.000000000000       0.138569980000       0.355570700000   
O       0.000000000000       0.187935770000      -1.074466460000  
H       0.882876920000      -0.383123830000       0.697839450000  
H      -0.882876940000      -0.383123830000       0.697839450000  
H       0.000000000000       1.145042790000       0.750208830000  
H       0.000000000000      -0.705300580000      -1.426986340000

Now start the calculation by executing:

pam  --mol=methanol.xyz --inp=hf.inp

If everything works fine the results of the calculation will be written to hf_methanol.out. In addition an archive file hf_methanol.tgz will be created. Depending on the type of calculation the archive file may include:

• DFCOEF containing molecular orbital coefficients and possibly energies.
• *.cube containing plots of molecular properties, typically electron densities, in the gridded Gaussian Cube format.
• Additional files for restarting particular types of calculations.

References

1. ↑ L. Visscher, Approximate molecular Dirac-Coulomb calculations using a simple Coulombic correction, Theor. Chem. Acc. 98, 68 (1997) electronic version.