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# Dielectric properties of Si

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## Task

Calculation of the static and frequency dependent dielectric properties of Si. Please have a look at the example on calculation of the static and frequency dependent dielectric properties of SiC first. The same procedures apply to this example.

## Input

### POSCAR

system Si 5.430 0.5 0.5 0.0 0.0 0.5 0.5 0.5 0.0 0.5 2 cart 0.00 0.00 0.00 0.25 0.25 0.25

### INCAR

- INCAR file for the static calculation:

## Static dielectric properties by means of DFPT #NBANDS = 4 #EDIFF = 1E-6 #LEPSILON = .TRUE. ## try to add this to the DFPT calculation #LPEAD = .TRUE. ## to get the ionic contributions to the ## static dielectric properties from ## perturbation theory #IBRION = 8 ## Static dielectric properties by means of PEAD #EDIFF = 1E-8 # finite field requires very tight convergence #LCALCEPS = .TRUE. #NELM = 100 ## Leave this in ISMEAR = 0 SIGMA = 0.01 GGA = PE

- INCAR for the frequency dependent calculation:

## Frequency dependent dielectric tensor without ## local field effects #ALGO = Exact #NBANDS = 64 #LOPTICS = .TRUE. ; CSHIFT = 0.1 #NEDOS = 2000 ## and you might try with the following #LPEAD = .TRUE. ## Frequency dependent dielectric tensor with and ## without local field effects in RPA and due to ## changes in the DFT xc-potential ## N.B.: beware one first has to have done a ## calculation with LOPTICS = .TRUE. (see above) #ALGO = CHI ; LSPECTRAL = .FALSE. #LRPA = .FALSE. ## be sure to take the same number of bands as for ## the LOPTICS = .TRUE. calculation, otherwise the ## WAVEDER file is not read correctly # NBANDS = 64 ## Leave this in ISMEAR = 0 SIGMA = 0.01 GGA = PE