LRC parameters

[Stephan]

Hello,
I'm about to use the LRC-kernel in order to calculate the dielectric function of a bulk solid.
There are some parameters which obviously belong to this kernel:
LRC_alpha:
This is the parameter occuring in the kernel. But how can I find a suitable value for my system?
lrc_fxc:
Can anybody tell me what's the meaning of this parameter?
FxcGRLx:
Do I need this parameter when I've already defined FxcGRLc?

Thank you and regards

Stephan

[Daniele Varsano]

Dear Stephan,
the alfa parameter is empirical, so it is system dependent.
The meaning is it somehow a way to include the screening of the system in just one parameter.
Anyway as a general issue I suggest you to read and study this kernel before using it also in order to understand if it is suitable and helpful for your research.

Here is the original reference:
PRL 88 066404 (2002)
Here an applications:
Phys. Rev. B 69, 155112 (2004).
PRB 82, 205319 (2010)

I presume that looking to who cites the original work may be you can see some range of values of alfa for different materials.
I'am not using this kernel so I can be wrong anyway the LRC_alpha is the only parameter to be specified together with NGsBlkXd, bands etc... as usual.

Best,
Daniele