Hartree-Fock

Header
Command-line arguments
- Definition
- Interpretation
Computation
Output

#+PROPERTY

In this example, we write a program that makes a Hartree-Fock calculation. The molecule is read in xyz format and a Gaussian atomic basis set in GAMESS format.

Header

module Command_line = Qcaml.Common.Command_line
module Util = Qcaml.Common.Util

let () =

Command-line arguments

We use the Command_line module to define the following possible arguments:

-b --basis : The name of the file containing the basis set
-x --xyz : The name of the file containing the atomic coordinates
-c --charge : The charge of the molecule
-m --multiplicity : The spin multiplicity

Definition

let open Command_line in
begin
set_header_doc (Sys.argv.(0));
set_description_doc "Computes the one- and two-electron hartree_fock on the Gaussian atomic basis set.";
set_specs
 [ { short='b' ; long="basis" ; opt=Mandatory;
arg=With_arg "<string>";
doc="Name of the file containing the basis set"; } ;
   
   { short='x' ; long="xyz" ; opt=Mandatory;
arg=With_arg "<string>";
doc="Name of the file containing the nuclear coordinates in xyz format"; } ;

   { short='m' ; long="multiplicity" ; opt=Optional;
     arg=With_arg "<int>";
     doc="Spin multiplicity (2S+1). Default is singlet"; } ;
   
   { short='c' ; long="charge" ; opt=Optional;
     arg=With_arg "<int>";
     doc="Total charge of the molecule. Specify negative charges with 'm' instead of the minus sign, for example m1 instead of -1. Default is 0"; } ;
   
 ]
end;

Interpretation

let basis_file  = Util.of_some @@ Command_line.get "basis" in
let nuclei_file = Util.of_some @@ Command_line.get "xyz" in

let charge =
match Command_line.get "charge" with
| Some x -> ( if x.[0] = 'm' then
               ~- (int_of_string (String.sub x 1 (String.length x - 1)))
             else
               int_of_string x )
| None   -> 0
in
 
let multiplicity =
match Command_line.get "multiplicity" with
| Some x -> int_of_string x
| None -> 1
in

Computation

We first read the xyz file to create a molecule:

let nuclei =
Qcaml.Particles.Nuclei.of_xyz_file nuclei_file
in

Then we create a Gaussian AO basis using the atomic coordinates:

let ao_basis =
Qcaml.Ao.Basis.of_nuclei_and_basis_filename ~nuclei basis_file
in

We create a simulation from the nuclei and the basis set:

let simulation = Qcaml.Simulation.make ~multiplicity ~charge ~nuclei ao_basis in

and we can make the Hartree-Fock computation:

let hf = Qcaml.Mo.Hartree_fock.make ~guess:`Huckel simulation in

Output

We print the convergence of the calculation:

Format.printf "@[%a@]" (Mo.Hartree_fock.pp) hf

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