(** Representation for two-electron operators expressed in a Gaussian basis set.  *)

open Constants

type t =
{
  coef_g     : float array;
  expo_g     : float array;
  expo_g_inv : float array;
}

let make coef_g expo_g =
  let expo_g_inv = 
      Array.map (fun x -> 1. /. x ) expo_g 
  in
  { coef_g ; expo_g ; expo_g_inv }


let one_over_r =
  
  let coef_g = [|
    841.88478132     ;  70.590185207     ;  18.3616020768    ;  7.2608642093    ;
    3.57483416444    ;  2.01376031082    ;  1.24216542801    ;  0.81754348620   ;
    0.564546514023   ;  0.404228610699   ;  0.297458536575   ;  0.223321219537  ;
    0.169933732064   ;  0.130190978230   ;  0.099652303426   ;  0.075428246546  ;
    0.0555635614051  ;  0.0386791283055  ;  0.0237550435652  ;  0.010006278387  ;
    |]
  and expo_g =
    [| 84135.654509    ;  2971.58727634    ;  474.716025959    ;  130.676724560    ;
        47.3938388887   ;  20.2078651631    ;  9.5411021938     ;  4.8109546955     ;
        2.52795733067   ;  1.35894103210    ;  0.73586710268    ;  0.39557629706    ;
        0.20785895177   ;  0.104809693858   ;  0.049485682527   ;  0.021099788990   ;
        0.007652472186  ;  0.0021065225215  ;  0.0003365204879  ;  0.0000118855674  |]
  in make coef_g expo_g