[Wien] Representative number for O2 energy

[Veronica Ganduglia Pirovano]

L. D. Marks wrote:

>On Fri, 11 Mar 2005, Veronica Ganduglia Pirovano wrote:
>
>  
>
>>I would  do exactly that see PRB 59, 15533 (1999)
>>I suggest an even higher cut off (30 Ry, at least!) for E_a and E_b.
>>I used 24 Ry and I know now that a somewhat larger cutoff gives an even
>>larger
>>number for the atomization energy.  The expected number is approx 3.1
>>eV/atom.
>>O has to be calculated in a NON-cubic box!  to get the right occupation!
>>    
>>

I think this is rather standard. You have 4 electrons (p) and three 
p-levels.
If the box is symmetric, you will populate 3 levels with electrons 'up' 
and the fourth will
result in a 1/3 occupation on each level 'down'.

Instead if the boy is not symmetry, thus breaking the px py pz symmetry 
you will
get one level doubly occupied and two single occupied: a triplet.

The O2 molecule has no problem because is not spherical even if 
calculated in a cubic box.

There are a few references on the 'non-spherical atoms', I would have to 
look. Nevertheless,
you have to take the lowest energy, and what I describe gives the lowest 
energy.

To the correction, my way of doing it, is substract the atom you put in, 
and compared that
with the 'best' O2 molecule you can calculate, usin in your notation E_b 
and E_a, but I recommend
you test the convergency with respect to cutoff ... you will be surprised.

Hope it helps.

>	Can you expand slightly on this comment; it might be useful for
>others (maybe I'm just being thick but I don't see why immediately).
>
>N.B., thanks also to Jeff Spirko. Extending his concept, one (I) could
>calculate the E as a function of distance to do a extrapolation.
>  
>
>>L. D. Marks wrote:
>>
>>    
>>
>>>I would like to get a representative energy (i.e. not the correct one, but
>>>one which is consistent with other calculations) for the O2 (molecule)
>>>energy for an RMT of 1.6 and RKMAX of 7, GGA. (These values are what I am
>>>using in some other calculations of bulk oxides, and the energy of O2
>>>has a significant effect on the theoretical heats of formation.) Obviously
>>>I cannot use these for the O2 molecule, the RMT has to be about 1.1. What
>>>I have done is:
>>>	a) Calculate O2 with RMT=1.1 RKMAX=5, ~30 a.u. cell: E_a
>>>	b) Calculate O  with RMT=1.1 RKMAX=5, ~30 a.u. cell: E_b
>>>	c) Calculate O  with RMT=1.6 RKMAX=7, ~30 a.u. cell: E_c
>>>Then estimate the effective O2 energy as
>>>	E_a - 2*E_b + 2*E_c
>>>
>>>I would be interested to know if anyone has a better idea/method, apart
>>>      
>>>
>>>from using 2*E_c + an experimental number for the bond energy (or
>>    
>>
>>>meta-GGA).
>>>
>>>-----------------------------------------------
>>>Laurence Marks
>>>Department of Materials Science and Engineering
>>>MSE Rm 2036 Cook Hall
>>>2220 N Campus Drive
>>>Northwestern University
>>>Evanston, IL 60201, USA
>>>Tel: (847) 491-3996 Fax: (847) 491-7820
>>>email: L - marks @ northwestern . edu
>>>http://www.numis.northwestern.edu
>>>-----------------------------------------------
>>>
>>>_______________________________________________
>>>Wien mailing list
>>>Wien at zeus.theochem.tuwien.ac.at
>>>http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>>>
>>>
>>>
>>>      
>>>
>>--
>>------------------------------------------------------------
>>            Dr. M. Veronica Ganduglia-Pirovano
>>	    Humboldt-Universitaet zu Berlin
>>	    Institut fuer Chemie
>>Post:   Unter den Linden 6
>>          10099 Berlin
>>
>>Besucher/   Brook-Taylor-Str. 2
>>Pakete:       12489 Berlin
>>
>>Tel.:           +(49) 30-2093-7139
>>Fax:           +(49) 30-2093-7136
>>e-mail:     vgp at chemie.hu-berlin.de
>>-------------------------------------------------------------
>>
>>
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>>Wien mailing list
>>Wien at zeus.theochem.tuwien.ac.at
>>http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>>
>>    
>>
>
>-----------------------------------------------
>Laurence Marks
>Department of Materials Science and Engineering
>MSE Rm 2036 Cook Hall
>2220 N Campus Drive
>Northwestern University
>Evanston, IL 60201, USA
>Tel: (847) 491-3996 Fax: (847) 491-7820
>email: L - marks @ northwestern . edu
>http://www.numis.northwestern.edu
>-----------------------------------------------
>
>_______________________________________________
>Wien mailing list
>Wien at zeus.theochem.tuwien.ac.at
>http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>
>  
>


-- 
------------------------------------------------------------
            Dr. M. Veronica Ganduglia-Pirovano
	    Humboldt-Universitaet zu Berlin
	    Institut fuer Chemie
Post:   Unter den Linden 6           
          10099 Berlin   

Besucher/   Brook-Taylor-Str. 2
Pakete:       12489 Berlin

Tel.:           +(49) 30-2093-7139
Fax:           +(49) 30-2093-7136
e-mail:     vgp at chemie.hu-berlin.de
-------------------------------------------------------------