NLO Tutorial

PART2-BERRY PHASE (in zero field)

Compute various quantities from Delta P

Four different steps

1. alas_zstar.in
Z* from finite difference of the polarization 
under atomic displacements

2. alas_ddk.in
Finite difference calculation of the ddk
(method of Na Sai with Marek's implementation)
Linear response calculation with finite difference ddk
Provides coherent number for comparison with
finite difference calculations of Z* and piezo coefficients

3. alas_piezo_clampedion.in
Clamped ion piezoelectric coefficients from finite difference 
calculation of the polarization under macroscopic strains
(ions fixed).

4. alas_piezo_relaxedion.in
Relaxed ion piezoelectric coefficients from finite difference 
calculation of the polarization under macroscopic strains
(relaxed ions).

