DFT+U periodicity-very confused results

[jbliu]

Dear Adimin,

The system of my present VASP job is Li-intercalated β-MnO2. A collinear ferromagnetic ordering is used in all our calculations. Valence electron configurations of the potentials were taken as 2s1 for Li, 3d6 4s1 for Mn, and 2s2 2p4 for O. But I find some very confused results.

I give “Structure A” a static calculation, the resulted energy is “-1228.8949 eV”. Then I put “Structure A” just translate 0.5 along direction “a” to get “Structure B”. But the resulted energy is “-1226.2272” after a static calculation! To my knowledge, “Structure A” and “Structure B” are just the same due to Periodic boundary conditions, isn’t it?

Could you help me to check it? Thank you very much!

The calculated results (GGA_PBE) are listed here:
energy (converged in steps) magn.moment
structureA -1228.8949 (58 DAVsteps) 170.9612
structureB -1226.2272 (159DAVsteps) 160.9582

Here are my input files:
INCAR:

SYSTEM = MnO2

LWAVE=.FALSE.
LCHARG=.FALSE.

LREAL= Auto

LASPH = .TRUE.

ISTART=0
ICHARG=2
ALGO=Normal
PREC=Normal

#LPLANE = .TRUE.
NPAR = 4
#LSCALU = .FALSE.
#NSIM = 4

ISPIN=2

ENCUT=500
ISMEAR=0
SIGMA=0.2

LDAU=.TRUE.
LDAUTYPE=2
LDAUL= -1 2 -1
LDAUU= 0.0 6.1 0.0
LDAUJ= 0.0 1.0 0.0

LORBIT=10

NELM=300

MAGMOM=120*0 60*1 1*0

KPOINTS:

AUTO GRID
0
M
2 1 1
0 0 0

POSCAR(structureA):

New structure
1.0
5.9780201912 0.0000000000 0.0000000000
0.0000000000 10.0517959595 0.0000000000
0.0000000000 0.0000000000 30.1553897858
O Mn Li
120 60 1
Direct
0.000000000 0.938843191 0.061156798
0.500000000 0.938843191 0.061156798
0.000000000 0.538843215 0.127823472
0.500000000 0.538843215 0.127823472
0.000000000 0.138843194 0.194490135
0.500000000 0.138843194 0.194490135
0.000000000 0.738843203 0.261156797
0.500000000 0.738843203 0.261156797
0.000000000 0.338843197 0.327823460
0.500000000 0.338843197 0.327823460
0.000000000 0.938843191 0.394490123
0.500000000 0.938843191 0.394490123
0.000000000 0.538843215 0.461156785
0.500000000 0.538843215 0.461156785
0.000000000 0.138843194 0.527823448
0.500000000 0.138843194 0.527823448
0.000000000 0.738843203 0.594490111
0.500000000 0.738843203 0.594490111
0.000000000 0.338843197 0.661156774
0.500000000 0.338843197 0.661156774
0.000000000 0.938843191 0.727823496
0.500000000 0.938843191 0.727823496
0.000000000 0.538843215 0.794490159
0.500000000 0.538843215 0.794490159
0.000000000 0.138843194 0.861156821
0.500000000 0.138843194 0.861156821
0.000000000 0.738843203 0.927823484
0.500000000 0.738843203 0.927823484
0.000000000 0.338843197 0.994490147
0.500000000 0.338843197 0.994490147
0.250000000 0.483470410 0.053718932
0.750000000 0.483470410 0.053718932
0.250000000 0.083470397 0.120385602
0.750000000 0.083470397 0.120385602
0.250000000 0.683470428 0.187052265
0.750000000 0.683470428 0.187052265
0.250000000 0.283470392 0.253718942
0.750000000 0.283470392 0.253718942
0.250000000 0.883470416 0.320385605
0.750000000 0.883470416 0.320385605
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0.750000000 0.483470410 0.387052268
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0.750000000 0.083470397 0.453718930
0.250000000 0.683470428 0.520385623
0.750000000 0.683470428 0.520385623
0.250000000 0.283470392 0.587052286
0.750000000 0.283470392 0.587052286
0.250000000 0.883470416 0.653718948
0.750000000 0.883470416 0.653718948
0.250000000 0.483470410 0.720385611
0.750000000 0.483470410 0.720385611
0.250000000 0.083470397 0.787052274
0.750000000 0.083470397 0.787052274
0.250000000 0.683470428 0.853718936
0.750000000 0.683470428 0.853718936
0.250000000 0.283470392 0.920385599
0.750000000 0.283470392 0.920385599
0.250000000 0.883470416 0.987052262
0.750000000 0.883470416 0.987052262
0.250000000 0.116529599 0.012947734
0.750000000 0.116529599 0.012947734
0.250000000 0.716529608 0.079614401
0.750000000 0.716529608 0.079614401
0.250000000 0.316529602 0.146281064
0.750000000 0.316529602 0.146281064
0.250000000 0.916529596 0.212947726
0.750000000 0.916529596 0.212947726
0.250000000 0.516529620 0.279614389
0.750000000 0.516529620 0.279614389
0.250000000 0.116529599 0.346281081
0.750000000 0.116529599 0.346281081
0.250000000 0.716529608 0.412947744
0.750000000 0.716529608 0.412947744
0.250000000 0.316529602 0.479614407
0.750000000 0.316529602 0.479614407
0.250000000 0.916529596 0.546281040
0.750000000 0.916529596 0.546281040
0.250000000 0.516529620 0.612947762
0.750000000 0.516529620 0.612947762
0.250000000 0.116529599 0.679614425
0.750000000 0.116529599 0.679614425
0.250000000 0.716529608 0.746281087
0.750000000 0.716529608 0.746281087
0.250000000 0.316529602 0.812947750
0.750000000 0.316529602 0.812947750
0.250000000 0.916529596 0.879614413
0.750000000 0.916529596 0.879614413
0.250000000 0.516529620 0.946281075
0.750000000 0.516529620 0.946281075
0.000000000 0.661156774 0.005509867
0.500000000 0.661156774 0.005509867
0.000000000 0.261156797 0.072176531
0.500000000 0.261156797 0.072176531
0.000000000 0.861156821 0.138843194
0.500000000 0.861156821 0.138843194
0.000000000 0.461156785 0.205509871
0.500000000 0.461156785 0.205509871
0.000000000 0.061156798 0.272176534
0.500000000 0.061156798 0.272176534
0.000000000 0.661156774 0.338843197
0.500000000 0.661156774 0.338843197
0.000000000 0.261156797 0.405509859
0.500000000 0.261156797 0.405509859
0.000000000 0.861156821 0.472176522
0.500000000 0.861156821 0.472176522
0.000000000 0.461156785 0.538843215
0.500000000 0.461156785 0.538843215
0.000000000 0.061156798 0.605509877
0.500000000 0.061156798 0.605509877
0.000000000 0.661156774 0.672176540
0.500000000 0.661156774 0.672176540
0.000000000 0.261156797 0.738843203
0.500000000 0.261156797 0.738843203
0.000000000 0.861156821 0.805509865
0.500000000 0.861156821 0.805509865
0.000000000 0.461156785 0.872176528
0.500000000 0.461156785 0.872176528
0.000000000 0.061156798 0.938843191
0.500000000 0.061156798 0.938843191
0.000000000 0.000000000 0.000000000
0.500000000 0.000000000 0.000000000
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0.500000000 0.200000003 0.133333340
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0.500000000 0.600000024 0.733333349
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0.750000000 0.500000000 0.166666672
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0.250000000 0.300000012 0.366666675
0.750000000 0.300000012 0.366666675
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0.750000000 0.899999976 0.433333337
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0.750000000 0.500000000 0.500000000
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[admin]

The translation of the cell does not play a role at all.
For the same structure (A and B) you have received two different
values of the total energy.
Different magnetic moments indicate that different electronic
configurations are formed.
1/ To fix the electronic configuration you can use NUPDOWN.
First you need to check which values should be fixed. Because Mn compounds
like high-spin configurations the magnetic moment will be app. 60*3=180.
The electron coming from Li will decrease the final magnetic moment.
Therefore check NUPDOWN values between 180 and say 170,
at which the most stable configuration is formed.
2/ Do not use high values of SIGMA. This allows the fractional filling of levels,
therefore again different configurations can be formed, and different
total energies are calculated. A high degree of degeneration (many
energy levels with similar energy) require the use of SIGMA as low
as 0.001.
3/ The cell is very asymmetric, c is 3-times longer than b.
Use the 3x3x1 (or 4x4x1) sampling.
4/ Because the final configuration is high-spin, do not set
the starting configuration low-spin. This makes the calculation
time-consuming. For Mn use MAGMOM 60*3 .

[jbliu]

Thank you for your useful advise!