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I am trying to do DFT+U calculation for the material BaLaMn2O6 . As per the vaspwiki it is recommended to set LMAXMIX = 4 (d-elements) and LMAXMIX = 6 (for f-elements) to obtain fast convergence to ground state. In my situation, I have both f-block element(La) and d-block element (Mn).

How should I set the LMAXMIX tag in the DFT+U calculation in proper way?

INCAR file

Global Parameters\
ISTART =  1            (Read existing wavefunction; if there)\
LREAL  = Auto          (Projection operators: automatic)\
ENCUT  =  600        (Cut-off energy for plane wave basis set, in eV)\
PREC   =  High       (Precision level)\
LWAVE  = .TRUE.        (Write WAVECAR or not)\
LCHARG = .TRUE.        (Write CHGCAR or not)\
ADDGRID= .TRUE.        (Increase grid; helps GGA convergence)\
EDIFF = 1.0E-06 \
ALGO=Fast\
Lattice Relaxation\
NSW    =  55          (number of ionic steps. Make it odd.)\
ISMEAR =  0            (gaussian smearing method )\
SIGMA  =  0.05         (please check the width of the smearing)\
IBRION =  2            (Algorithm: 0-MD; 1-Quasi-New; 2-CG)\
ISIF   =  2            (optimize atomic coordinates and lattice parameters)\
EDIFFG = -1.0E-03      (Ionic convergence; eV/AA)\
PREC   =  High         (Precision level)\
\
LDAU = True             #switches on DFT+U  \
LDAUJ = 0 0 0 0         # J values (For LDAUTYPE=2 , Ueff = U-J)\
LDAUL = 3 -1 2 -1       #l-quantum number (-1 : no U)\
LDAUPRINT = 1           # 0:silent, 1: write occupancy matrix to OUTCAR)\ 
LDAUTYPE = 2            #The simplified approach to the DFT+U , introduced by  Dudarev et al.\
LDAUU = 4.0 0 3.0 0     # for Ba:0 , Mn:5.0 , Sb:0, F:0 ( U values in eV) \
LMAXMIX = 6             # 4 for d-electrons, 6 for f-electrons\
LASPH = .TRUE.   \

POSCAR file

generated by phonopy\
   1.0\
     3.9178000000000002    0.0000000000000000    0.0000000000000000\
     0.0000000000000000    3.9178000000000002    0.0000000000000000\
     0.0000000000000000    0.0000000000000000    7.8070000000000004\
La Ba Mn O\
   1    1    2    6\
Direct\
  0.0000000000000000  0.0000000000000000  0.0000000000000000\
  0.0000000000000000  0.0000000000000000  0.5000000000000000\
  0.5000000000000000  0.5000000000000000  0.7548999999999999\
  0.5000000000000000  0.5000000000000000  0.2451000000000001\
  0.5000000000000000  0.5000000000000000  0.0000000000000000\
  0.0000000000000000  0.5000000000000000  0.7626999999999999\
  0.5000000000000000  0.0000000000000000  0.7626999999999999\
  0.0000000000000000  0.5000000000000000  0.2373000000000001\
  0.5000000000000000  0.0000000000000000  0.2373000000000001\
  0.5000000000000000  0.5000000000000000  0.5000000000000000
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    $\begingroup$ If you want to include only the d orbitals in the projection, you can set LMAXMIX = 4. This would exclude the f orbitals from the projection. If you want to include both the d and f orbitals in the projection, you should set LMAXMIX = 6. This would include both the f and d orbitals. Pay attention that You should always consider what electrons the elements you are studying have in their valence shell regardless of the block they blong to. $\endgroup$ Nov 11, 2023 at 3:41
  • $\begingroup$ Thank you for your response. But Mn has electronic configuration : [Ar] 3d5 4s2 and for La the configuration : [Xe] 5d1 6s2 , here the valence shell electrons are both s-orbitals. That means should i not use the DFT+ U scenario or should i use the U parameter for only Mn ? $\endgroup$
    – user192399
    Nov 11, 2023 at 6:06
  • $\begingroup$ @JaafarMehrez can you please give me a reference for setting LMAXMIX =6 to include both d- and f- electrons ? Like where such example is used or any example mentioned in vaspwiki or in vasp community . Just to be sure. Thank You !! $\endgroup$
    – user192399
    Nov 20, 2023 at 10:00
  • $\begingroup$ @JaafarMehrez can i set LMAXMIX = 6 2 4 2 ,for elements in POSCAR i.e, La Ba Mn O respectively ? $\endgroup$
    – user192399
    Nov 20, 2023 at 10:07
  • $\begingroup$ From vaspwikit the tag LMAXMIX takes one integer, it states exactly LMAXMIX 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. I think by choosing the value to 6 you already included other l-quantum numbers. $\endgroup$ Nov 20, 2023 at 10:22

1 Answer 1

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DFT+U is an advanced computational method developed specifically to enhance the accuracy of describing systems containing strongly correlated d or f electrons. These systems, such as antiferromagnetic NiO, often pose challenges for conventional LDA and GGA functionals, which tend to provide inaccurate description.

When applying DFT+U in VASP, the parameter LMAXMIX plays a crucial role in controlling the range of l-quantum numbers for which the one-center PAW charge densities are processed and saved in the CHGCAR file. Unlike LDAUL or LDAUJ, which accept multiple values as an integer array, LMAXMIX is a single integer value. To accurately capture the effects of f-block elements in your system, it is recommended to set LMAXMIX=6. Thus, by choosing the value to 6, you already included other l-quantum numbers. However, it's important to note that this choice can lead to increased computational complexity.

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