# This code is part of a Qiskit project.
#
# (C) Copyright IBM 2020, 2023.
#
# This code is licensed under the Apache License, Version 2.0. You may
# obtain a copy of this license in the LICENSE.txt file in the root directory
# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
#
# Any modifications or derivative works of this code must retain this
# copyright notice, and modified files need to carry a notice indicating
# that they have been altered from the originals.
"""FCIDump"""
from __future__ import annotations
from dataclasses import dataclass
from pathlib import Path
from typing import Sequence
import numpy as np
from qiskit_nature import QiskitNatureError
from qiskit_nature.second_q.operators.symmetric_two_body import SymmetricTwoBodyIntegrals
from .dumper import _dump_1e_ints, _dump_2e_ints, _write_to_outfile
[docs]@dataclass
class FCIDump:
"""
Qiskit Nature dataclass for representing the FCIDump format.
The FCIDump format is partially defined in Knowles1989.
References:
Knowles1989: Peter J. Knowles, Nicholas C. Handy,
A determinant based full configuration interaction program,
Computer Physics Communications, Volume 54, Issue 1, 1989, Pages 75-83,
ISSN 0010-4655, https://doi.org/10.1016/0010-4655(89)90033-7.
"""
num_electrons: int
"""The number of electrons."""
hij: np.ndarray
"""The alpha 1-electron integrals."""
hijkl: SymmetricTwoBodyIntegrals
"""The alpha/alpha 2-electron integrals ordered in chemist' notation."""
hij_b: np.ndarray | None = None
"""The beta 1-electron integrals."""
hijkl_bb: SymmetricTwoBodyIntegrals | None = None
"""The beta/beta 2-electron integrals ordered in chemist' notation."""
hijkl_ba: SymmetricTwoBodyIntegrals | None = None
"""The beta/alpha 2-electron integrals ordered in chemist' notation."""
constant_energy: float | None = None
"""The constant energy comprising (for example) the nuclear repulsion energy and inactive
energies."""
multiplicity: int = 1
"""The multiplicity."""
orbsym: Sequence[int] | None = None
"""A list of spatial symmetries of the orbitals."""
isym: int = 1
"""The spatial symmetry of the wave function."""
@property
def num_orbitals(self) -> int:
"""The number of orbitals."""
return self.hij.shape[0]
[docs] @classmethod
def from_file(cls, fcidump: str | Path) -> FCIDump:
"""Constructs an FCIDump object from a file.
Args:
fcidump: Path to the input file.
Returns:
A :class:`.FCIDump` instance.
"""
# pylint: disable=cyclic-import
from .parser import _parse
return _parse(fcidump if isinstance(fcidump, Path) else Path(fcidump))
[docs] def to_file(self, fcidump: str | Path) -> None:
"""Dumps an FCIDump object to a file.
Args:
fcidump: Path to the output file.
Raises:
QiskitNatureError: not all beta-spin related matrices are either None or not None.
QiskitNatureError: if the dimensions of the provided integral matrices do not match.
"""
outpath = fcidump if isinstance(fcidump, Path) else Path(fcidump)
# either all beta variables are None or all of them are not
if not all(h is None for h in [self.hij_b, self.hijkl_ba, self.hijkl_bb]) and not all(
h is not None for h in [self.hij_b, self.hijkl_ba, self.hijkl_bb]
):
raise QiskitNatureError("Invalid beta variables.")
if set(self.hij.shape) != set(self.hijkl.shape):
raise QiskitNatureError(
"The number of orbitals of the 1- and 2-body matrices do not match: "
f"{set(self.hij.shape)} vs. {set(self.hijkl.shape)}"
)
norb = self.hij.shape[0]
nelec = self.num_electrons
einact = self.constant_energy
ms2 = self.multiplicity - 1
mos = range(norb)
with outpath.open("w", encoding="utf8") as outfile:
# print header
outfile.write(f"&FCI NORB={norb:4d},NELEC={nelec:4d},MS2={ms2:4d},\n")
if self.orbsym is None:
outfile.write(" ORBSYM=" + "1," * norb + ",\n")
else:
if len(self.orbsym) != norb:
raise QiskitNatureError(f"Invalid number of orbitals {norb} {len(self.orbsym)}")
outfile.write(" ORBSYM=" + ",".join(str(o) for o in self.orbsym) + ",\n")
outfile.write(f" ISYM={self.isym:d},\n&END\n")
# append 2e integrals
_dump_2e_ints(self.hijkl, mos, outfile)
if self.hijkl_ba is not None:
_dump_2e_ints(np.transpose(self.hijkl_ba), mos, outfile, beta=1)
if self.hijkl_bb is not None:
_dump_2e_ints(self.hijkl_bb, mos, outfile, beta=2)
# append 1e integrals
_dump_1e_ints(self.hij, mos, outfile)
if self.hij_b is not None:
_dump_1e_ints(self.hij_b, mos, outfile, beta=True)
# TODO append MO energies (last three indices are 0)
# append inactive energy
if einact is not None:
_write_to_outfile(outfile, einact, (0, 0, 0, 0))