Charged system IO3-

[armando_derezende]

Dear VASP users,

I want to calculate an IO3- molecule. I am using the following tags in the INCAR:

• SYSTEM = IO3
  NSW = 1000
  LREAL = .FALSE.
  IALGO = 48
  ISMEAR = 0
  IBRION = 1
  ISIF = 2
  NSIM = 1
  ISYM=0
  ENCUT=800
  PREC=Accurate
  EDIFF = 1E-7
  EDIFFG = -1E-5
  IVDW=12
  NELECT=78
  LDIPOL=.TRUE.
  ADDGRID=.TRUE.

The NELECT=78 comes from 53 + 3*8 +1, for iodine, oxygen and negative charge, respectively.
The calculation runs, but the total energy comes out positive. I have a similar structure HIO3 calculated with similar INCAR (without NELECT and LDIPOL tags), that returns reasonable -21 eV as total energy. I also use this energy in formation reactions and have good results. As HIO3 has neutral charge, the problem must be with NELECT and LDIPOL.

What would be a good combination of tags to solve this problem?
My version is vasp.5.4.4

Thank you very much!

Best regards,
Armando

The POTCARS I am using are:

• PAW_PBE I 08Apr2002
  PAW_PBE O 08Apr2002

The POSCAR is:

IO3
1.0
20.0 0.0 0.0
0.0 20.0 0.0
0.0 0.0 20.0
I O
1 3
Direct
0.5000000 0.5000000 0.5000000
0.5103823 0.4853520 0.5900256
0.4093707 0.4920826 0.4877244
0.5145500 0.5902457 0.4915599

[fabien_tran1]

Hi,

Your value for NELECT is not correct. By default NELECT is the number of valence electrons (the sum of the ZVAL in POTCAR), i.e. the core electrons are not taken into account. NELECT should be 7+3*6+1=26.

[armando_derezende]

Thank you Mr Fabien!

It is working now. Have a nice day.