type t = {
  charge : Charge.t;
  electrons : Electrons.t ;
  basis : Basis.t;
  nuclei : Nuclei.t;
  overlap : Overlap.t lazy_t;
  overlap_ortho : Orthonormalization.t lazy_t;
  eN_ints : NucInt.t lazy_t;
  kin_ints : KinInt.t lazy_t;
  ee_ints : ERI.t lazy_t;
  nuclear_repulsion : float;
}

let make ?multiplicity:(multiplicity=1) ?charge:(charge=0) ~nuclei basis =
  let electrons =
    Electrons.make ~multiplicity ~charge nuclei
  in
  let charge = 
    Array.fold_left (fun accu (e, _) -> accu + Charge.to_int (Element.to_charge e) )
      0 nuclei - Electrons.(electrons.n_alpha + electrons.n_beta)
    |> Charge.of_int
  in
  let overlap = 
    lazy (Overlap.of_basis basis)
  in
  {
    charge ; 
    basis ; nuclei ; electrons ; overlap ;
    overlap_ortho = lazy (Orthonormalization.make (Lazy.force overlap));
    eN_ints  = lazy (NucInt.of_basis_nuclei basis nuclei);
    kin_ints = lazy (KinInt.of_basis basis);
    ee_ints  = lazy (ERI.of_basis basis);
    nuclear_repulsion =  Nuclei.repulsion nuclei;
  }


let of_filenames ?multiplicity:(multiplicity=1) ?charge:(charge=0) ~nuclei basis =
  let nuclei =
    Nuclei.of_filename ~filename:nuclei
  in
  let basis =
    Basis.of_nuclei_and_basis_filename ~nuclei ~filename:basis
  in
  make ~charge ~multiplicity ~nuclei basis