GAMMA
The GAMMA file is an input file used with the ICHARG=5 tag. It is read by VASP during an electronic minimization to incorporate additional occupation changes per k-point and orbital before calculating a new charge density. The file's format is structured as follows:
567 -1 ! Number of k-points, default number of bands 1 81 92 ! k-point index, band window of occupations to be added -0.88697620213424 -0.00000000000110 0.00952263319978 -0.00013538025816 -0.00003023919061 0.00036153047962 … ! 1 nbnd row per line 0.00952263319978 0.00013538025816 -0.90621349117750 -0.00000000000092 -0.00002036611614 0.00020787085249 … … (10 more lines) 2 81 92 -0.89265621432703 -0.00000000000107 -0.00944765243065 -0.00671452451385 -0.00029309275635 -0.00012146585216 … (11 more lines) … 567 82 91 -0.89056253498876 -0.00000000000112 -0.00449699353373 0.00290102672201 -0.00014095045304 0.00000787119531 -0.00289794970644 …
The file contains a small header marking the number of k-points (must be consistent with the current number of k-points in the irreducible Brillouin zone), and if there is a default number of bands to be assumed per k-point. Next, is a line that increments the k-point index and the band window, i.e. the indices of bands for which the occupation changes are read in. This is followed by the actual occupation changes as a nband times nband matrix (one row per line), where complex number formatting is used, first number is the real part and the second is the complex part, third is again real part, etc.
While ICHARG=5 is set, VASP will read this file right before the new charge density is calculated. However, VASP will only read the file if an additional file called vasp.lock is present in the current directory. This design is such to allow an interface to an external code that performs in each SCF step some extra computation and updates the KS occupations.
The TRIQS software package[1] makes use of it to perform charge self-consistent DFT plus dynamical mean field theory (DMFT) calculations[2][3], and provides tutorials on how to perform such calculations with VASP[4][5].
Related tags and articles
References
- ↑ O. Parcollet, M. Ferrero, T. Ayral, H. Hafermann, I. Krivenko, L. Messio and P. Seth, Computer Physics Communications 196, 398 (2015).
- ↑ M. E. Merkel, A. Carta, S. Beck and Alexander Hampel, Journal of Open Source Software 7, 77 (2022).
- ↑ M. Aichhorn, L. Pourovskii, P. Seth, V. Vildosola, M. Zingl, O. E. Peil, X. Deng, J. Mravlje, G. J. Kraberger, C. Martins, M. Ferrero, O. Parcollet, Computer Physics Communications 204, 200 (2016).
- ↑ triqs.github.io/dft_tools/latest/tutorials.html#vasp-interface-examples (2024).
- ↑ triqs.github.io/solid_dmft/tutorials/PrNiO3_csc_vasp_plo_cthyb/tutorial (2024).