[Pw_forum] trend in HOMO-LUMO energies

[Rajdeep Banerjee]

Dear all,
             this is a question about the reliability of the trend in
HOMO-LUMO energies produced by GGA calculation. I know the absolute
HOMO-LUMO energies produced by GGA cannot be trusted.

Let us assume a model system where I have a set of clusters of different
sizes and an adsorbate molecule. I want to compare the HOMO-LUMO energies
of the molecule and the cluster with respect to vacuum (before the
adsorbate gets attached to the cluster to get an idea of the charge
transfer beforehand.)

Now, my question is, would GGA be able to correctly produce the trend in
the relative position of the adsorbate and cluster HOMO-LUMO energies (wrt
vacuum) as we increase the cluster size?

If not, what are the possible choices to get a correct trend?


I appreciate any help in this regard. Thanks in advance.

best,
-- 
Rajdeep Banerjee
PhD student
JNCASR, Bangalore
India
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