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 [math]\displaystyle{ -\partial f^0/\partial \epsilon }[/math]. Formally, the integration window [math]\displaystyle{ [\mu-e,\mu+e] }[/math] is chosen such that
- [math]\displaystyle{ \int_{\mu-e}^{\mu+e} \left(-\frac{\partial f^0}{\partial \epsilon}\right) d\epsilon = 1 - \alpha, }[/math]
where [math]\displaystyle{ \alpha \equiv }[/math] ELPH_TRANSPORT_DFERMI_TOL. This gives
- [math]\displaystyle{ e = k_B T \, \ln\!\left(\tfrac{2-\alpha}{\alpha}\right). }[/math]
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.