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 $-\partial f^0/\partial \epsilon$ . Formally, the integration window $[\mu-e,\mu+e]$ is chosen such that

{\displaystyle \int_{\mu-e}^{\mu+e} \left(-\frac{\partial f^0}{\partial \epsilon}\right) d\epsilon = 1 - \alpha, }

where $\alpha \equiv$ ELPH_TRANSPORT_DFERMI_TOL. This gives

{\displaystyle e = k_B T \, \ln\!\left(\tfrac{2-\alpha}{\alpha}\right). }

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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