[gpaw-users] Delta SCF Method

[Hongliang Xin]

Dear GPAW Users,

Recently, I am trying to use the linear expansion Delta SCF method in GPAW
to look at the excitation of O2 molecule on metal surfaces. Basically, I
intend to look at the transition of electron from Fermi level into the 2pi
antibonding state of O2. This case is a little bit more complicated than CO
and N2 since 2pi states are degenerate and half occupied. So I have two
questions related to this script:

1. How to differentiate spin up and spin down in the set-up? I thought spin
0 is spin up, and spin1 is for spin down. But from the example on GPAW
website, it has reversed notation. So for O2, I set up like this shown
below.
lumo = c_mol.get_pseudo_wave_function(band=5, kpt=0, spin=1)
dscf.dscf_calculation(calc, [[1.0, orbital, 1]], atoms)

2. From the description of the method, I know that the wave function of
unoccupied state to be excited are described as linear combination of K-S
states. For 2pi anti-bonding state, the K-S state above the Fermi level is
used for linear expansion. So my question is that how many extra band I
should include in the GPAW calculator. Or does it affect the accuracy of
this method? There is convergence problem as I set the nbands too large.

Thanks,

Hongliang


-- 
Hongliang Xin
Ph.D. Candidate
Dept. of Chemical Engineering
University of Michigan
3166 HH Dow
2300 Hayward
Ann Arbor, MI 48109
Phone: (734) 647-8051
E-mail: hxin at umich.edu
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