Integrals

Header
Command-line arguments
- Definition
- Interpretation
Computation
Output

#+PROPERTY

In this example, we write a program that reads the geometry of a molecule in xyz format and a Gaussian atomic basis set in GAMESS format. The output is a set of files containing the one- and two- electron integrals.

Header

module Command_line = Qcaml.Common.Command_line
module Util = Qcaml.Common.Util
open Qcaml.Linear_algebra

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
-u --range-separation : The value of $\mu$, the range-separation parameter in range-separated DFT. If this option is not present, no output file will be generated for the range-separated integrals.

Definition

let open Command_line in
begin
set_header_doc (Sys.argv.(0));
set_description_doc "Computes the one- and two-electron integrals 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='u' ; long="range-separation" ; opt=Optional;
arg=With_arg "<float>";
doc="Range-separation parameter."; } ;
 ]
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 range_separation =
match Command_line.get "range-separation" with
| None -> None
| Some mu -> Some (float_of_string mu)
in

let operators =
match range_separation with
| None -> []
| Some mu -> [ Qcaml.Operators.Operator.of_range_separation mu ]
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 an Gaussian AO basis using the atomic coordinates, and we optionally introduce the range-separation parameter via the operators:

let ao_basis =
Qcaml.Ao.Basis.of_nuclei_and_basis_filename ~kind:`Gaussian
  ~operators ~cartesian:true ~nuclei basis_file
in

We compute the required one-electron integrals:

let overlap   = Qcaml.Ao.Basis.overlap   ao_basis in
let eN_ints   = Qcaml.Ao.Basis.eN_ints   ao_basis in
let kin_ints  = Qcaml.Ao.Basis.kin_ints  ao_basis in
let multipole = Qcaml.Ao.Basis.multipole ao_basis in
let x_mat     = multipole "x" in
let y_mat     = multipole "y" in
let z_mat     = multipole "z" in

and the two-electron integrals (1/r and long range):

let ee_ints   = Qcaml.Ao.Basis.ee_ints   ao_basis in
let lr_ints   = 
match range_separation with
| Some _mu -> Some (Qcaml.Ao.Basis.ee_lr_ints ao_basis)
| None -> None
in

Output

We write the one-electron integrals:

Matrix.to_file ~filename:"overlap.dat" ~sym:true overlap;
Matrix.to_file ~filename:"eN.dat" ~sym:true eN_ints;
Matrix.to_file ~filename:"kinetic.dat" ~sym:true kin_ints;
Matrix.to_file ~filename:"x.dat" ~sym:true x_mat;
Matrix.to_file ~filename:"y.dat" ~sym:true y_mat;
Matrix.to_file ~filename:"z.dat" ~sym:true z_mat;

and the the two-electron integrals:

Four_idx_storage.to_file ~filename:"eri.dat" ee_ints;
match lr_ints with
| Some integrals -> Four_idx_storage.to_file ~filename:"eri_lr.dat" integrals;
| None -> ()

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