[Wien] BaTiO3.vcoul

[John Rundgren]

Dear All,
With option R2V in BaTiO3.in0, BaTiO3.vcoul is written out. It is interesting to compare the files
 
radius times BaTiO3.vsp 
radius squared times BaTiO3.vcoul (spherical part)

The files start with the values given in the Table below:

Atom    Z    r*vsp    r*vcoul
Ba      56   -111.3   -400.8
Ti        22   -43.0    -157.8
O         8    -15.6    - 60.4

As User's Guide 4.2 says, vsp is in units of Rydbergs and r*vsp is approximately -2*Z. But what units and what approximation are used for r*vcoul ? User's Guide and the comments of file BaTiO3.vcoul are silent on this point.

I had expected that r*vcoul/Z would be v_e_r_y close to an integer. Isn't it true that the centre of an atom is the same whether the atom is free or situated in a crystal ?
Best regards,
John

John Rundgren
Department of Theoretical Physics, Royal Institute of Technology (KTH),
AlbaNova University Center, SE-10691 Stockholm, Sweden
fax +46 8 5537 8216, voice +46 8 5537 8171,
home page http://www.theophys.kth.se/~jru