# This file is part of dxtb.
#
# SPDX-Identifier: Apache-2.0
# Copyright (C) 2024 Grimme Group
#
# 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
#
# http://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
# limitations under the License.
"""
Vibrational Analysis: IR Spectra
================================
Calculate IR intensities from the geometric dipole derivative.
"""
from __future__ import annotations
import torch
from tad_mctc.math import einsum
from tad_mctc.units import AU2KMMOL
from dxtb._src.typing import Any, Literal, NoReturn, Tensor
from .result import BaseResult
__all__ = ["ir_ints", "IRResult"]
[docs]
class IRResult(BaseResult):
"""
Data from the calculation of an IR spectrum.
- Vibrational frequencies
- IR intensities
"""
converter_ints: dict[str, float] = {
"a.u.": 1.0,
"km/mol": AU2KMMOL,
}
__slots__ = ["_ints", "_ints_unit"]
def __init__(
self,
freqs: Tensor,
ints: Tensor,
device: torch.device | None = None,
dtype: torch.dtype | None = None,
) -> None:
"""
Initialize the IR result.
Parameters
----------
freqs : Tensor
Vibrational frequencies in atomic units.
ints : Tensor
IR intensities in atomic units.
device : torch.device | None, optional
Device of the tensors. If ``None``, the device of `freqs` is used.
Defaults to ``None``.
dtype : torch.dtype | None, optional
Data type of the tensors. If ``None``, the data type of `freqs` is
used. Defaults to ``None``.
"""
super().__init__(
freqs=freqs,
device=device if device is not None else freqs.device,
dtype=dtype if dtype is not None else freqs.dtype,
)
self._ints = ints
self._ints_unit = "a.u."
# intensities
@property
def ints(self) -> Tensor:
return self._ints * self.converter_ints[self._ints_unit]
@ints.setter
def ints(self, *_: Any) -> NoReturn:
raise RuntimeError(
"Setting IR intensities is not supported. Internally, the "
"intensities should always be stored in atomic units. Use "
"the `to_unit` method to convert to a different unit or set the "
"`ints_unit` attribute."
)
@property
def ints_unit(self) -> str:
return self._ints_unit
@ints_unit.setter
def ints_unit(self, value: str) -> None:
if value not in self.converter_ints:
raise ValueError(f"Unsupported intensity unit: {value}")
self._ints_unit = value
# conversion
[docs]
def to_unit(self, value: Literal["freqs", "ints"], unit: str) -> Tensor:
"""
Convert a value from one unit to another based on the converter dictionary.
"""
if value == "freqs":
return self._convert(self.freqs, unit, self.converter_freqs)
if value == "ints":
return self._convert(self.ints, unit, self.converter_ints)
raise ValueError(f"Unsupported value for conversion: {value}")
[docs]
def use_common_units(self) -> None:
"""
Convert the frequencies and intensities to common units, that is,
`cm^-1` for frequencies and `km/mol` for intensities.
"""
self.freqs_unit = "cm^-1"
self.ints_unit = "km/mol"
[docs]
def ir_ints(dmu_dr: Tensor, modes: Tensor) -> Tensor:
"""
Calculate IR intensities from the geometric dipole derivative.
Parameters
----------
dmu_dr : Tensor
Dipole derivative tensor of shape `(..., 3, nat, 3)`.
modes : Tensor
Normal modes of shape `(..., nat*3, nmodes)`.
Returns
-------
Tensor
IR intensities of shape `(..., nfreqs)`.
"""
# reshape for matmul: (..., 3, nat, 3) -> (..., 3, nat*3)
dmu_dr = dmu_dr.view(*(*modes.shape[:-2], 3, -1))
# convert cartesian to internal coordinate derivatives
# (..., 3, nat*3) @ (..., nat*3, nfreqs) = (..., 3, nfreqs)
dmu_dq = dmu_dr @ modes
# square deriv and sum along cartesian components for intensity
# (..., 3, nfreqs) * (..., 3, nfreqs) -> (..., nfreqs)
return einsum("...xf,...xf->...f", dmu_dq, dmu_dq)
