QCaml/Basis/Overlap.ml

open Util
open Constants

(** Computes all the overlap integrals of the contracted shell pair *)
let contracted_class shell_a shell_b : float Zmap.t = 

  let shell_p =
    Shell_pair.create_array shell_a shell_b
  in

  (* Pre-computation of integral class indices *)
  let class_indices = 
    Angular_momentum.zkey_array (Angular_momentum.Doublet
                                   Contracted_shell.(totAngMom shell_a, totAngMom shell_b))
  in

  let contracted_class = 
    Array.make (Array.length class_indices) 0.
  in

  (* Compute all integrals in the shell for each pair of significant shell pairs *)

  for ab=0 to (Array.length shell_p - 1)
  do
    let coef_prod =
      shell_p.(ab).Shell_pair.coef 
    in
    (** Screening on thr product of coefficients *)
    if (abs_float coef_prod) > 1.e-4*.cutoff then
      begin
        let center_ab = 
          shell_p.(ab).Shell_pair.center_ab 
        in
        let center_pa = 
          shell_p.(ab).Shell_pair.center_a
        in
        let expo_inv = 
          shell_p.(ab).Shell_pair.expo_inv
        in
        let norm_coef_scale =
          shell_p.(ab).Shell_pair.norm_coef_scale
        in

        Array.iteri (fun i key ->
            let (angMomA,angMomB) =
              let a = Zkey.to_int_array Zkey.Kind_6 key in
              ( [| a.(0) ;  a.(1) ;  a.(2) |], 
                [| a.(3) ;  a.(4) ;  a.(5) |] )
            in
            let f k = 
              Overlap_primitives.hvrr (angMomA.(k), angMomB.(k)) 
                expo_inv
                (Coordinate.coord center_ab k,
                 Coordinate.coord center_pa k) 
            in
            let norm =  norm_coef_scale.(i) in
            let integral = chop norm (fun () -> (f 0)*.(f 1)*.(f 2)) in 
            contracted_class.(i) <- contracted_class.(i) +. coef_prod *. integral
          ) class_indices
      end
  done;
  let result = 
    Zmap.create (Array.length contracted_class)
  in
  Array.iteri (fun i key -> Zmap.add result key contracted_class.(i)) class_indices;
  result





(** Write all overlap integrals to a file *)
let to_file ~filename basis =
  let to_int_tuple x = 
    let open Zkey in
    match to_int_tuple Kind_3 x with
    | Three x -> x
    | _ -> assert false
  in

  let oc = open_out filename in
  for i=0 to (Array.length basis) - 1 do
    print_int (Contracted_shell.index basis.(i)) ; print_newline ();
    for j=0 to i do
      (* Compute all the integrals of the class *)
      let cls =
        contracted_class basis.(i) basis.(j) 
      in

      (* Write the data in the output file *)
      Array.iteri (fun i_c powers_i ->
          let i_c = Contracted_shell.index basis.(i) + i_c + 1 in
          let xi = to_int_tuple powers_i in
          Array.iteri (fun j_c powers_j ->
              let j_c = Contracted_shell.index basis.(j) + j_c + 1 in
              let xj = to_int_tuple powers_j in
              let key = 
                Zkey.of_int_tuple (Zkey.Six (xi,xj))
              in
              let value = 
                try
                  Zmap.find cls key 
                with Not_found -> failwith "Bug in overlap integrals"
              in
              if (abs_float value > cutoff) then
                Printf.fprintf oc "%4d %4d %20.12e\n"
                  i_c j_c value
            ) (Contracted_shell.powers basis.(j))
        ) (Contracted_shell.powers basis.(i));
    done;
  done;
  close_out oc