[gpaw-users] Lattice parameter with GGA or GGA+U ?

[Zhenhua Zeng]

Hi Jun,

Consider the big scaling value in lattice constant (0.9), there may be 
some problem in you script. V is not a element that so U demanding. 
Basically, U is not necessary to get the approximate lattice constant of 
3d transitional metal oxides. Why not post you script and keep whether 
your parameters are convergent or not?

Zhenhua

On 2012/5/22 11:31, Ole Jess Stausholm-Møller wrote:
> Typically the +U gives larger lattice parameters, and these typically
> scale with the value of U applied, so as you increase U you also
> increase the lattice parameters. Naturally the larger value of U the
> larger magnetic moments you typically also get. So I guess that you
> could use the +U, but you have to have some reason to use a particular
> range of U values. Say your fix point is a magnetic moment of 3, then
> you should use the U value that gives you this magnetic moment and
> then check the sensitivity of your results the applied value of U.
>
> /Jess
>
> Quoting jun yan<junyan at stanford.edu>:
>
>> Hi,
>>
>>       I am trying to get the lattice parameter for VO, which has a
>> very simple structure of atoms = bulk('VO', 'rocksalt', a=4.46)
>> The following is what I got with PBE using spinpol=True.  The
>> OV_0.90000 means scaling lattice parameter a=4.46 with 0.9 .
>>
>> OV_0.90000.txt:Total Magnetic Moment: 1.956392
>> OV_0.95000.txt:Total Magnetic Moment: 2.448952
>> OV_1.00000.txt:Total Magnetic Moment: 2.600094
>> OV_1.05000.txt:Total Magnetic Moment: 2.638621
>>
>> OV_0.90000.txt:Free Energy:    -16.24786
>> OV_0.95000.txt:Free Energy:    -16.24359
>> OV_1.00000.txt:Free Energy:    -16.20235
>> OV_1.05000.txt:Free Energy:    -16.11876
>>
>> so as the lattice parameter becomes small, the total energy
>> decreases with decreasing magnetic moment. But this is wrong. The
>> expected lattice parameter will be around a=4.46, (scaling factor
>> 1.0) and with magnetic moment 3.0.
>>
>> My question is should I use GGA+U to get lattice parameters ?  If
>> so, should I use the same U for all the scaling factors ? I expect
>> that if the cell becomes smaller, the d-electrons interactions
>> change and thus requires a different U…  and even if I use the same
>> U, would different U gives different lattice parameter ?
>>
>>   I appreciate if someone with more experiences would like to shine
>> some light.
>>
>> All the best,
>> Jun
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