[xcrysden] About isovalue

[Scott Beckman]

The charge is not calculated at EFermi, but it is the sum of the charge 
from the Kohn-Sham states integrated over the Brillouin zone and summed 
from the lowest state to the EFermi. 

The integral over the charge distribution (on your XSF grid) should 
equal "nelec" from PWSCF. 

The minimum and maximum value tells you the min. and max. value on the 
XSF grid.  So if you have a uniform charge concentration min=max.  For 
Si it is likely that 0.0014 will be located somewhere in an interstitial 
region and 0.87 will be located in a bond-charge. 

I wouldn't say that there is any "ideal" isovalue.  I would fiddle with 
this value and look at the charge distribution.  This will allow you to 
develop qualitative picture of how your system works. 





Yamit wrote:
> Hello All
>
> I am using Xcrysden to plot charge density of Silicon (example 05: 
> Quantum Esspresso-4.2).
> *) Could anyone please tell the details of "xsf" file?
> ( This charge density is calculated at Fermi Energy. Please also 
> correct me, if I am wrong.)
>
> *)When for Silicon: Minimum grid value :0.001411 and
> Maximum grid value : 0.87371
> What should be the ideal isovalue? Are there any rules to select the 
> isovalues, from the values in *.xsf file?
>
> (For isovalue of 0.001411(min) & 0.87371(max), no charge density has 
> been found. )
>
> Thank you in advance!!!
>
> Regards
> Amit N. Harode
> CRL INDIA
>
> P.S.
> Input file for QE's pp.x is as follows, &inputpp
> prefix = 'si'
> filplot = 'sicharge'
> plot_num= 0
> /
> &plot
> nfile = 1
> filepp(1) = 'sicharge'
> weight(1) = 1.0
> iflag = 3
> output_format = 5
> fileout = 'si.rho.xsf'
> /
>
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>
>
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