Chimie Théorique » QMX

from math import pi, sqrt

import numpy as np

class DOS:

    def __init__(self, calc, width=0.1, window=None, npts=201):

        """Electronic Density Of States object.

        calc: calculator object

            Any ASE compliant calculator object.

        width: float

            Width of guassian smearing.

        window: tuple of two float

            Use ``window=(emin, emax)``.  If not specified, a window

            big enough to hold all the eigenvalues will be used.

        npts: int

            Number of points.

        """

        self.npts = npts

        self.width = width

        self.w_k = calc.get_k_point_weights()

        self.nspins = calc.get_number_of_spins()

        self.e_skn = np.array([[calc.get_eigenvalues(kpt=k, spin=s)

                                for k in range(len(self.w_k))]

                               for s in range(self.nspins)])

        self.e_skn -= calc.get_fermi_level()

        if window is None:

            emin = self.e_skn.min() - 5 * self.width

            emax = self.e_skn.max() + 5 * self.width

        else:

            emin, emax = window

        self.energies = np.linspace(emin, emax, npts)

    def get_energies(self):

        """Return the array of energies used to sample the DOS."""

        return self.energies

    def delta(self, energy):

        """Return a delta-function centered at 'energy'."""

        x = -((self.energies - energy) / self.width)**2

        return np.exp(x) / (sqrt(pi) * self.width)

    def get_dos(self, spin=None):

        """Get array of DOS values.

        The *spin* argument can be 0 or 1 (spin up or down) - if not

        specified, the total DOS is returned.

        """

        if spin is None:

            if self.nspins == 2:

                # Spin-polarized calculation, but no spin specified -

                # return the total DOS:

                return self.get_dos(spin=0) + self.get_dos(spin=1)

            else:

                spin = 0

        dos = np.zeros(self.npts)

        for w, e_n in zip(self.w_k, self.e_skn[spin]):

            for e in e_n:

                dos += w * self.delta(e)

        return dos