TAUCAR

The TAUCAR file stores kinetic-energy density

[math]\displaystyle{ \tilde \tau_{\sigma\sigma'} = \frac{\hbar^2}{2m} \sum_{n\mathbf{k}} f_{n\mathbf{k}} \mathbf{\nabla} \tilde \psi_{n\mathbf{k}\sigma} \cdot \nabla \tilde \psi_{n\mathbf{k}\sigma'} }[/math]

in VASP units (eV [math]\displaystyle{ \AA^{-3} }[/math]), i.e. the valence contribution of the pseudo expectation value on the plane-wave grid. Here, [math]\displaystyle{ \mathbf{\nabla} \tilde \psi_{n\mathbf{k}\sigma} }[/math] is the gradient of the pseudo Kohn-Sham orbitals within the PAW method. The TAUCAR file is written by default for a metaGGA calculation, but it can also be written for XC functionals that are independent of [math]\displaystyle{ \tau }[/math] by setting LTAU = T. The kinetic energy density can also be redirected to vaspwave.h5 using LH5.

To avoid writing [math]\displaystyle{ \tau }[/math] for a metaGGA calculation use LCHARG = F. This controls the writing of both the charge density and the kinetic energy density.

The TAUCAR file (together with the CHGCAR file) can be read to restart a calculation (ICHARG).

Tip: We recommend starting from the density files when repeatedly restarting with small changes in the input parameters, e.g., the k-point mesh (KPOINTS).

Mind: Available as of VASP 6.6.

Format

The format is the same as the CHGCAR file except for the lack of augmentation occupancies. In other words the TAUCAR file consists of the following block:

• Structure in POSCAR format
• FFT-grid dimensions NGXF, NGYF, NGZF
• Kinetic energy density

Magnetic calculations

For magnetic calculations, the TAUCAR file contains additional data blocks for the magnetic part of [math]\displaystyle{ \tau }[/math]. For spin-polarized calculations (ISPIN=2), the two blocks are the kinetic-energy density of the two spin channels, [math]\displaystyle{ \tau_\uparrow }[/math] followed by [math]\displaystyle{ \tau_\downarrow }[/math]. For noncollinear calculations (LNONCOLLINEAR=T), the first block is the total kinetic-energy density and the remaining three are the magnetic part [math]\displaystyle{ \mathbf{\tau}_m }[/math] in the spinor basis set by SAXIS.

Related tags and articles

Restart and output files cheat sheet

CHGCAR, LTAU, ICHARG,

FFT-grid dimensions: ENCUT, NGXF, NGYF, NGZF