[Pw_forum] about superposition of atomic rho and atomic wfc's

[Stefano de Gironcoli]

Dear Reza Ebraahimi,

Quoting Reza Ebraahimi <rezaebraahimi at yahoo.com>:
> Hi
> I am new with pwscf, so sorry if my question seems basic to you!
> i have noticed that the code calculates the superpositon of charge   
> density and wfc's from atomic configurations by two subroutines:   
> "atomic_rho.f90" and "atomic_wfc.f90". Could anyone refer me to a   
> text or something to know exactly what happens in these two( i mean   
> mathematically)?

atomic_rho builds the charge density from superposition of atomic  
charges in reciprocal space as the product of the spherical fourier  
transform of the atomic charge and the structure factor of each atomic  
species and then tranform them in real space.
atomic_wfc does the same for the wfcs with some variations due to the  
fact that wfcs correspond to a given angular momentum.

To understand the coded formulas it may be useful to have at hand the  
expansion of a plane wave in terms of spherical harmonics and bessel  
functions that one can find in basic book on quantum mechanics.

> And i thought that we need the superposition of charge density from   
> atomic configuration to build up the KS Hamiltonian( with the   
> knowledge of n(r) ) and obtain the solid wfc's by diagonalizing it   
> at the first iteration. Why do we need the superposition of wfc's   
> from atomic configuration?

Iterative diagonalizations require a starting guess.
The code allows you to choose among atomic or random...

> Thank You


Don't forget to provide your affiliation

best regards,

Stefano de Gironcoli - SISSA and DEMOCRITOS






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