(** Electron-electron repulsion integrals *)

open Constants
open Util

module Zm = struct

  let name = "Electron repulsion integrals"

  let zero_m ~maxm ~expo_p_inv ~expo_q_inv ~norm_pq_sq =
    let expo_pq_inv = expo_p_inv +. expo_q_inv in
    assert (expo_pq_inv <> 0.);
    let norm_pq_sq = 
      if norm_pq_sq > integrals_cutoff then norm_pq_sq else 0.
    in
    let exp_pq = 1. /. expo_pq_inv in
    let t = norm_pq_sq *. exp_pq in
    let f = two_over_sq_pi *. (sqrt exp_pq) in
    let result = boys_function ~maxm t in
    let rec aux accu k = function
      | 0 -> result.(k) <- result.(k) *. accu
      | l -> 
        begin
          result.(k) <- result.(k) *. accu;
          let new_accu = -. accu *. exp_pq in
          aux new_accu (k+1) (l-1)
        end
    in
    aux f 0 maxm;
    result

end

module M = TwoElectronIntegrals.Make(Zm) 
include M