Discrepancy in wiki with LMAXMIX and LMAXTAU?

[matthewkuner]

wiki/index.php/LMAXMIX
wiki/index.php/LMAXTAU

Based on the info in the wiki, for a calculation with only d-elements, you would want to set LMAXMIX=4 and LMAXTAU=6.

However, the description for LMAXMIX says it "controls up to which l-quantum number the one-center PAW charge densities are passed through the charge density mixer and written to the CHGCAR file."
and the description for LMAXTAU says it "is the maximum l-quantum number included in the PAW one-center expansion of the kinetic energy density."

Why are these not both recommended to be set to the same value?

Separately, should one consider what "block" the elements are in, or whether a structure has a certain type of electrons? I.e. I understand for Zinc that it is both a d-block element and has up to d-electrons. However, Gallium is a p-block element but has d-electrons--what should be done in a case like Gallium?

[jonathan_lahnsteiner2]

Dear matthewkuner,

I am not sure if I understand the question that you are asking. LMAXTAU is a parameter for the expansion of the kinetic energy density. The kinetic energy is the second derivative of the wave function.
The LMAXMIX tag controls up to which quantum number the one-center PAW charge densities are passed trough the charge density mixer.
So you control two different things with these parameters and therefore their default values will be different.

You should always consider what electrons the elements you are studying have in their valence shell. So Zinc and Gallium both posses d-electrons in their valence shell. So you should use the same LMAXMIX for both of them.

I hope this helps to answer your questions.
All the best Jonathan

[matthewkuner]

Hi Jonathan,

Thanks for your reply! Let me rephrase. From the wiki, I believe it is acceptable to set the following:

For materials with up to s electrons, you can set LMAXMIX = LMAXTAU = 0
For materials with up to p electrons, you can set LMAXMIX = LMAXTAU = 2
For materials with up to d electrons, you can set LMAXMIX = LMAXTAU = 4
For materials with up to f electrons, you can set LMAXMIX = LMAXTAU = 6

Is this correct?

Best,
Matthew

[jonathan_lahnsteiner2]

Dear Matthew,

If you check the vasp wiki wiki/index.php/LMAXTAU you can see the following recommended values for LMAXTAU
for s-elements: LMAXTAU=2, for p: LMAXTAU=4, and for d: LMAXTAU=6. It also says you should use the default value,
except if you have f-electron systems where I would recommend to use LMAXTAU=8.

The recommended values for the tag LMAXMIX can be found on the vasp wiki too wiki/index.php/LMAXMIX
Those depend on the details of your calculation, as if you are doing a LDA+U calculation or maybe you are using non-collinear calculations.
There it says for example if you are doing LDA+U, that you should set LMAXMIX to 4 for d-electrons (or 6 for f-elements). If you don't have f or d electrons
just use the default value.


All the best Jonathan