# Lint as: python3
# Copyright 2019 DeepMind Technologies Limited. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
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"""Basic definition of units and converters useful for chemistry."""

from typing import Union
import numpy as np

# 1 Bohr = 0.52917721067 (12) x 10^{-10} m
# https://physics.nist.gov/cgi-bin/cuu/Value?bohrrada0
# Note: pyscf uses a slightly older definition of 0.52917721092 angstrom.
ANGSTROM_BOHR = 0.52917721067
BOHR_ANGSTROM = 1. / ANGSTROM_BOHR

# 1 Hartree = 627.509474 kcal/mol
# https://en.wikipedia.org/wiki/Hartree
KCAL_HARTREE = 627.509474
HARTREE_KCAL = 1. / KCAL_HARTREE


def bohr2angstrom(x_b: Union[float, np.ndarray]) -> Union[float, np.ndarray]:
  return x_b * ANGSTROM_BOHR


def angstrom2bohr(x_a: Union[float, np.ndarray]) -> Union[float, np.ndarray]:
  return x_a * BOHR_ANGSTROM


def hartree2kcal(x_b: Union[float, np.ndarray]) -> Union[float, np.ndarray]:
  return x_b * KCAL_HARTREE


def kcal2hartree(x_a: Union[float, np.ndarray]) -> Union[float, np.ndarray]:
  return x_a * HARTREE_KCAL
