QCaml/Basis/Overlap.ml

open Util
open Constants
open Lacaml.D

type t = Mat.t

module Am  = Angular_momentum
module Bs  = Basis
module Co  = Coordinate
module Cs  = Contracted_shell
module Csp = ContractedShellPair
module Sp  = ShellPair

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

  let shell_p =
    Csp.create shell_a shell_b
  in

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

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

  let sp =
    shell_p.Csp.shell_pairs
  in
  let center_ab = 
    shell_p.Csp.center_ab
  in
  let norm_coef_scale =
    shell_p.Csp.norm_coef_scale
  in

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

  for ab=0 to (Array.length sp - 1)
  do
    let coef_prod =
      shell_p.Csp.coef.(ab) 
    in
    (** Screening on thr product of coefficients *)
    if (abs_float coef_prod) > 1.e-4*.cutoff then
      begin
        let expo_inv = 
          shell_p.Csp.expo_inv.(ab)
        in
        let center_pa = 
          sp.(ab).Sp.center_a
        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 = 
              let xyz = match k with
              | 0 -> Co.X
              | 1 -> Co.Y
              | _ -> Co.Z
              in
              Overlap_primitives.hvrr (angMomA.(k), angMomB.(k)) 
                expo_inv
                (Co.get xyz center_ab,
                 Co.get xyz center_pa) 
            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


(** Create overlap matrix *)
let of_basis basis =
  let to_powers x = 
    let open Zkey in
    match to_powers Kind_3 x with
    | Three x -> x
    | _ -> assert false
  in

  let n     = basis.Bs.size 
  and shell = basis.Bs.contracted_shells 
  in

  let result = Mat.create n n in
  for j=0 to (Array.length shell) - 1 do
    for i=0 to j do
      (* Compute all the integrals of the class *)
      let cls =
        contracted_class shell.(i) shell.(j) 
      in

      Array.iteri (fun j_c powers_j ->
          let j_c = shell.(j).index + j_c + 1 in
          let xj = to_powers powers_j in
          Array.iteri (fun i_c powers_i ->
              let i_c = shell.(i).index + i_c + 1 in
              let xi = to_powers powers_i in
              let key = 
                Zkey.of_powers (Zkey.Six (xi,xj))
              in
              let value = 
                try Zmap.find cls key 
                with Not_found -> failwith "Bug in overlap integrals"
              in
              result.{i_c,j_c} <- value;
              result.{j_c,i_c} <- value;
            ) shell.(i).powers
        ) shell.(j).powers
    done;
  done;
  Mat.detri result;
  result




(** Write all overlap integrals to a file *)
let to_file ~filename overlap =

  let oc = open_out filename in
  let n =
    Mat.dim1 overlap 
  in

  for j=1 to n  do
    for i=1 to j do
      if (abs_float overlap.{i,j} > cutoff) then
        Printf.fprintf oc "%4d %4d %20.12e\n" i j overlap.{i,j}
    done;
  done;
  close_out oc