ASE Manual Release 3.6.1.2825 CAMd - CampOS Wiki

ASE Manual, Release 3.6.1.2828
7.20 Infrared intensities
InfraRed is an extension of Vibrations, in addition to the vibrational modes, also the infrared intensities of
the modes are calculated for an Atoms object.
class ase.infrared.InfraRed(atoms, indices=None, name=’ir’, delta=0.01, nfree=2, directions=None)
Class for calculating vibrational modes and infrared intensities using finite difference.
The vibrational modes are calculated from a finite difference approximation of the Dynamical matrix and
the IR intensities from a finite difference approximation of the gradient of the dipole moment. The method
is described in:
D. Porezag, M. R. Pederson: “Infrared intensities and Raman-scattering activities within densityfunctional
theory”, Phys. Rev. B 54, 7830 (1996)
The calculator object (calc) linked to the Atoms object (atoms) must have the attribute:
>>> calc.get_dipole_moment(atoms)
In addition to the methods included in the Vibrations class the InfraRed class introduces
two new methods; get_spectrum() and write_spectra(). The summary(), get_energies(),
get_frequencies(), get_spectrum() and write_spectra() methods all take an optional method keyword. Use
method=’Frederiksen’ to use the method described in:
T. Frederiksen, M. Paulsson, M. Brandbyge, A. P. Jauho: “Inelastic transport theory from firstprinciples:
methodology and applications for nanoscale devices”, Phys. Rev. B 75, 205413
(2007)
atoms: Atoms object The atoms to work on.
indices: list of int List of indices of atoms to vibrate. Default behavior is to vibrate all atoms.
name: str Name to use for files.
delta: float Magnitude of displacements.
nfree: int Number of displacements per degree of freedom, 2 or 4 are supported. Default is 2 which will
displace each atom +delta and -delta in each cartesian direction.
directions: list of int Cartesian coordinates to calculate the gradient of the dipole moment in. For example
directions = 2 only dipole moment in the z-direction will be considered, whereas for directions = [0,
1] only the dipole moment in the xy-plane will be considered. Default behavior is to use the dipole
moment in all directions.
Example:
>>> from ase.io import read
>>> from ase.calculators.vasp import Vasp
>>> from ase.infrared import InfraRed
>>> water = read(’water.traj’) # read pre-relaxed structure of water molecule
>>> calc = Vasp(prec=’Accurate’,
... ediff=1E-8,
... isym=0,
... idipol=4, # calculate the total dipole moment
... dipol=water.get_center_of_mass(scaled=True),
... ldipol=True)
>>> water.set_calculator(calc)
>>> ir = InfraRed(water)
>>> ir.run()
>>> ir.summary()
-------------------------------------
Mode Frequency Intensity
# meV cm^-1 (D/Å)^2 amu^-1
-------------------------------------
150 Chapter 7. Documentation for modules in ASE