LVTOT-tag, and core level shifts

Default

LVTOT

=

.FALSE.

This tag determines whether the total local potential (file LOCPOT) is written. Starting from version VASP 4.4.4, VASP also calculates the average electrostatic potential at each ion. This is done, by placing a test charge with the norm 1, at each ion and calculating

$$\bar V_n = \int V({\bf r}) \rho_{\rm test} (\vert{\bf r}- {\bf R_n}\vert) d^3 {\bf r}$$

The spatial extend of the test charge is determined by ENAUG (see Sec. 6.9), so that calculations can be compared only if ENAUG is kept fixed. The change of the core level shift $\Delta c$ between to models can be calculated by the simple formula

$$\Delta c= \bar V^1_n - \epsilon_{\rm Fermi}^1 - ( \bar V^2_n - \epsilon_{\rm Fermi}^2 ),$$

where $V^1_n$ and $V^2_n$ are the electrostatic potentials at the core of an ion for the first and second calculations, respectively, and $\epsilon_{\rm Fermi}^1$ and $\epsilon_{\rm Fermi}^2$ are the Fermi levels in these calculations. Clearly, the core level shift is the same for all core electrons in this simple approximation. In addition, screening effects are not taken into account.