My Community

I calculate the lattic parameter of bcc sodium using ultrasoft pseudopotential lda ,the experiment date is 4.29 ,however tha calculated date is 4.04,is there any problem?
the following is the input file. I know using ISIF =3 to calcuate the lattic parameter is not a best method ,but I want to know if my input file has any problem.
thank you in advance
INCAR
PREC = High
ENCUT=450
EDIFF = 1.0D-06
EDIFFG = 1.0D-03
ISMEAR = 1
SIGMA=0.2
ALGO=V
IBRION = 2
ISIF = 3
ISYM = 1
NSW = 81
PSTRESS=0
POTIM=0.1
KPOINTS
PREC = High
ENCUT=450
EDIFF = 1.0D-06
EDIFFG = 1.0D-03
ISMEAR = 1
SIGMA=0.2
ALGO=V
IBRION = 2
ISIF = 3
ISYM = 1
NSW = 81
PSTRESS=0
POTIM=0.1

POSCAR
sodium
4.00000000000000
1.0115083471292077 0.0000000000000000 0.0000000000000000
0.0000000000000000 1.0115083471292077 0.0000000000000000
0.0000000000000000 0.0000000000000000 1.0115083471292077
2
Direct
0.0000000000000000 0.0000000000000000 0.0000000000000000
0.5000000000000000 0.5000000000000000 0.5000000000000000
KPOINTS
mesh
0
Monkhorst-Pack
28 28 28
0 0 0

this is the typical LDA overbinding, the relaxed lattice constants are always too small by several percent.

thank you very much ,