Linear Response

Name MagneticGaugeCorrection
Section Linear Response
Type integer
Default gipaw

For magnetic linear response: how to handle gauge-invariance in the description of the coupling of electrons to the magnetic field.

Options:

• none:
  No correction.
  
• gipaw:
  GIPAW correction: C Pickard and F Mauri, Phys. Rev. Lett. 91, 196401 (2003).
  
• icl:
  ICL correction: S Ismail-Beigi, EK Chang, and SG Louie, Phys. Rev. Lett. 87, 087402 (2001).
  

Name ResponseMethod
Section Linear Response
Type integer
Default sternheimer

Some response properties can be calculated either via Sternheimer linear response or by using finite differences. You can use this variable to select how you want them to be calculated, it applies to em_resp and vib_modes calculation modes. By default, the Sternheimer linear-response technique is used.

Options:

• sternheimer:
  The linear response is obtained by solving a self-consistent Sternheimer equation for the variation of the orbitals. This is the recommended method.
  
• finite_differences:
  Properties are calculated as a finite-differences derivative of the energy obtained by several ground-state calculations. This method, slow and limited only to static response, is kept mainly because it is simple and useful for testing purposes.