ELPH_TRANSPORT_DFERMI_TOL

ELPH_TRANSPORT_DFERMI_TOL = [real]
Default: ELPH_TRANSPORT_DFERMI_TOL = 1e-6

Description: choose the fraction of the integral weight of the derivative of the Fermi–Dirac distribution that is excluded when defining the energy window for the Onsager coefficients. Must be between 0 and 1, and is only used when ELPH_TRANSPORT_DRIVER=1.

Mind: Available as of VASP 6.5.0

Using this parameter, ELPH_TRANSPORT_EMIN and ELPH_TRANSPORT_EMAX are automatically computed from the chemical potentials and the distribution $- \partial f^{0} / \partial ϵ$ . Formally, the integration window $[μ - e, μ + e]$ is chosen such that

\int_{μ - e}^{μ + e} (- \frac{\partial f^{0}}{\partial ϵ}) d ϵ = 1 - α,

where $α \equiv$ ELPH_TRANSPORT_DFERMI_TOL. This gives

e = k_{B} T \ln (\frac{2 - α}{α}) .

A small value means that only the tails of the derivative of the Fermi-dirac distribution are excluded from the integral. A large value means that only a small energy window around the chemical potential is used.

The integral is then discretized with a number of energy points set by TRANSPORT_NEDOS and evaluated using the Simpson's rule.

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