XANES in Diamond

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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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