XANES in Diamond

(UNDER CONSTRUCTION)

Overview > XANES in Diamond > List of tutorials

Task

Calculation of the XANES K-edge in diamond using the supercell core-hole method.

Input

POSCAR

cubic diamond
 3.567
0.5 0.5 0.0
0.0 0.5 0.5
0.5 0.0 0.5
 2
direct
0.0 0.0 0.0
0.25 0.25 0.25

We will not use this structure as input but rather use it to construct a super cell from it that is actually used in the calculations.

INCAR

System = DIAMOND
ALGO = FAST
ISMEAR = 0; SIGMA = 0.1;
ICORELEVEL = 2
CLNT = 1
CLN = 1
CLL = 0
CLZ = 1.0
CH_LSPEC = .TRUE.
CH_SIGMA = 0.5
NBANDS = 300
LREAL = A

To promote a core electron into the conduction bands and hence create the core-hole ICORELEVEL=2 has to be set. This corresponds to the final state approximation
CLNT=1 selects the first atom species in the POSCAR file.
CLN=1 selects main quantum number 1 (hence K-edge).
CLL=0 selects angular quantum number 0 (s).
CLZ=1.0 selects the charge of the core hole. By setting this number to a fractional value we can mimick different screening of the electrons. Since this purely exploits error cancellation and the physical background of non-integer charges is not defined well, it should be only used with caution.
By setting CH_LSPEC=.TRUE. we enable the calculation of matrix elements between core and conduction states and the calculation of the core electron absorption spectrum.
The broadening of the core electron absorption spectrum is controlled by the tag CH_SIGMA. Usually it is good practice to set this value low and broaden the spectrum in post processing.
We have to set NBANDS to a larger value to consider enough conduction band states in the calculation.
Since super cells are used the calculation of the projection operators in real space is much faster, hence LREAL=A is set.

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Overview > XANES in Diamond > List of tutorials

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