Elphem

Fix
`elph/electron_phonon.py`
Wrong wave-vectors in the calculation of coupling constants were fixed:
$$\mathbf{q} + \mathbf{G}_1 - \mathbf{G}_2 \to \mathbf{q} + \mathbf{G}_2 - \mathbf{G}_1.$$

New Features
Three types of coupling constants are available:
- Bloch coupling constants [1]
- Nordheim coupling constants [2]
- Bardeen coupling constants [3]

[1] F. Bloch, Z. Phys. **52**, 555–600 (1929).
[2] L. Nordheim, Ann. Phys. (Berlin) **401**, 607–640 (1931).
[3] J. Bardeen, Phys. Rev. **52**, 688–697 (1937).

Due to the failure of the v0.3.0 release to PyPI

Features
Currently, Elphem allows calculations of
- direct and reciprocal lattice vectors from lattice constants with optimization.
- electronic structures with empty lattice approximation.
- phonon dispersion relations with Debye model.
- first-order electron-phonon couplings.
- one-electron self-energies.
- spectral functions with(out) normalization.

Crystal Structures
3D
- Simple cubic
- Face-centered cubic
- Body-centered cubic
- Hexagonal

2D
- Square
- Hexagonal

1D
- Line

Features
Currently, Elphem allows calculations of
- direct and reciprocal lattice vectors from lattice constants with optimization.
- electronic structures with empty lattice approximation.
- phonon dispersion relations with Debye model.
- first-order electron-phonon couplings.
- one-electron self-energies.
- spectral functions with(out) normalization.

Crystal Structures
3D
- Simple cubic
- Face-centered cubic
- Body-centered cubic
- Hexagonal

2D
- Square
- Hexagonal

1D
- Line

**El**ectron-**Ph**onon Interactions with **Em**pty Lattice

Features
Currently, Elphem allows calculations of
- (reciprocal) lattice vectors from lattice constants.
- electronic structures with empty lattice approximation.
- phonon dispersion relations with Debye model.
- first-order electron-phonon couplings.
- one-electron self-energies.
- spectral functions.


test
Release Test