[CPMD-list] orbitals with RHOOUT BANDS

[Axel Kohlmeyer]

On Fri, 22 Jul 2005, Eneritz Muguruza wrote:

EM> Dear CPMD users,

hi eneritz,

EM> 
EM>       I have some doubts about the orbitals in CPMD. I have plotted the
EM> occupied
EM>  orbitals of a molecule of 20 atoms by calculating first the KOHN-SHAM ENERGIES
EM> (with no additional empty states) and using the RHOOUT BANDS keyword in the
EM> &CPMD section. And I get some orbitals. When I do the same calculation but
EM> without calculating the Kohn-sham energies, I get different results, some of
EM> them agree with the ones in the previous calculation but others seem to be
EM> linear combinations of them.  
EM> Is this because in the second case (without calculating the KS energies) the KS
EM> matrix is not diagonalized and the orbitals obtained are linear combinations of
EM> the eigenfunctions?   

CPMD normally only enforces that the KS-orbitals are orthogonal. 
with a KS-energies run, you diagonalize them, yielding the 
canonical orbitals.

EM> When I repeat the same calculations with a simple molecule like water the two
EM> ways yield the same orbitals.

well, diagonal orbitals are also orthogonal in such a
simple case you may get former while looking for the latter.

EM> 
EM> What is the difference with the Wannier functions?

this will yield localized orbitals by transforming the orbitals
in a way that the centers of the orbitals are maximally apart. 
this is similar to a boys-localization with a gaussian basis 
set. see, e.g.:
http://www.theochem.ruhr-uni-bochum.de/~axel.kohlmeyer/cpmd-vmd/part5.html#chap7_sect2
for a very simple example (the image on the left hand side shows four
localized orbitals of water: two sigma-bonds, two lone pairs).

regards,
	axel.

EM> 
EM>      Thank you very much in advance,
EM> 
EM>                
EM>                Eneritz
EM> 

-- 

=======================================================================
Dr. Axel Kohlmeyer   e-mail: axel.kohlmeyer at theochem.ruhr-uni-bochum.de
Lehrstuhl fuer Theoretische Chemie          Phone: ++49 (0)234/32-26673
Ruhr-Universitaet Bochum - NC 03/53         Fax:   ++49 (0)234/32-14045
D-44780 Bochum  http://www.theochem.ruhr-uni-bochum.de/~axel.kohlmeyer/
=======================================================================
If you make something idiot-proof, the universe creates a better idiot.