sigmas variable

NAME

  sigmas -width of the confinement operator

DESCRIPTION

The sigmas variable enters the expression of the confinement operator which is added to the Kohn-Sham hamiltonian when computing the stress tensor (when stress is set to ON). The confinement operator is diagonal in the plane wave basis and ensures that the resolution used for the description of the wavefunctions is independent of cell size.

H_conf(G) = facs * 0.5 * G2 * (1 - f((0.5*G2 - ecuts)/sigmas))

f(E) = 1 / ( 1 + exp(E) )
 

The effect of the confinement operator is to reduce the amplitude of the wavefunctions' Fourier coefficients for large wave vectors (G2 > ecuts).

DEFAULT VALUE

1

ALLOWED VALUES

positive floating point

RELATED INFORMATION

stress, facs, ecuts, refcell,


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