Metagga MS2 gives positive free energy

[richard_kang]

Hello,

I am a relatively new user to VASP, and I have recently installed vasp6.2.0.

I was initially going to do a calculation of a 2x2 supercell of Ag fcc with fairly larger brillouin zone (8x8x30 Angstroms in cartesian) but I was concerned that the free energy is giving me a positive value (about 5eV), which gave me fairly negative free energies when using PBE (around -55 eV). I decided to do a Ag atom in a box to see if I am using MS2 correct, and it turns out that this is also giving me a positive energy (about 2.9eV). I tried PBE0 and PBE, but these are giving me negative energies... so I wasn't sure if I putting the settings wrong. below is my INCAR:

IBRION = -1
NSW = 0

ISTART = 0 ! No reading
ISPIN = 2 ! Spin-polarized
MAGMOM = 0.5
EDIFF = 1E-6 ! Units in eV

ENCUT = 500
METAGGA = MS2

PREC = Normal ! standard precision
ISMEAR = 0 ! Gaussian Smear
LREAL = AUTO

Any insight on this would very appreciated. I am also using a PAW_PBE POTCAR.

[ferenc_karsai]

You should start from a preconverged WAVECAR file with PBE (ISTART=1).
Also activate LASPH=.TRUE.

Good tips for metagga calculations are written at the end of the METAGGA wiki site:
wiki/index.php/METAGGA#cite_note-sun:jcp:12-3

[richard_kang]

Thank you for the reply.

Maybe I might have posted the wrong INCAR, but the reading of the PBE WAVECAR and LASPH = .TRUE. gave me a positive free energy on a simple 2x2 supercell of Silver fcc, and thus I tried with a simple Ag in a box, with the INCAR provided in the post. I recognize that I did not read the PBE WAVECAR in that case, but this is what I was going for in the original try:

SYSTEM = Ag fcc (100) pulled 0

IBRION = -1
NSW = 0

ISTART = 1 ! Read the PBE wavefunction
NUPDOWN = 2 ! Triplet Initial Guess
ISPIN = 2 ! Spin-polarized
EDIFF = 1E-6 ! Units in eV
MAGMOM = 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.380

ENCUT = 500
LORBIT = 11
METAGGA = MS2
LASPH =.TRUE.

PREC = Normal ! standard precision
ISMEAR = 0 ! Gaussian Smear
LREAL = AUTO

[ferenc_karsai]

I ran your atom in the box calculation and could reproduce your result without having a previous PBE calculation. Only when I had a previous PBE calculation and continued from that calculation I got proper negative energies.

Could you upload your other example too?

[richard_kang]

Yes, sorry I should have posted earlier:
The following zip file includes the files used except INCAR for both PBE and MS2 cases.

inputs-agslab.zip

The stdouts for these two are also included -- named "pbe-0.err" for PBE and "ms2-0.err" for the subsequent MS2.

INCARs I used are in the following:
For PBE

Code: Select all

SYSTEM = Ag fcc (100) pulled 0

IBRION = -1
NSW = 0

NUPDOWN = 2   ! Triplet Initial Guess
ISPIN = 2 ! Spin-polarized
EDIFF = 1E-6  ! Units in eV
MAGMOM = 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.380

ENCUT = 500
LASPH = .TRUE.
LORBIT = 11
GGA = PE

PREC = Normal    ! standard precision
ISMEAR = 0 ! Gaussian Smear
LREAL = AUTO

For the subsequent MS2 job I did this:

Code: Select all

SYSTEM = Ag fcc (100) pulled 0

IBRION = -1
NSW = 0

ISTART = 1    ! Read the PBE wavefunction
NUPDOWN = 2   ! Triplet Initial Guess
ISPIN = 2     ! Spin-polarized
EDIFF = 1E-6  ! Units in eV
MAGMOM = 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.380

ENCUT = 500
LORBIT = 11
METAGGA = MS2
LASPH =.TRUE.

ALGO = ALL
PREC = Normal ! standard precision
ISMEAR = 0 ! Gaussian Smear
LREAL = AUTO

Thank you very much for looking into my post!
I really appreciate it.

[ferenc_karsai]

Indeed I could reproduce your calculations, but I talked to colleagues and one important thing was pointed out.
The energies of the atoms in the POTCAR file are subtracted from the total energies.
The energies of the POTCARs are obtained from PBE. But when we go to another potential in our case METAGGAs the energies can be of different order. So the absolute value of the total energies is completely meaningless and only relative energies are meaningful.

The calculation is most likely ok since the calculation seems to converge.