optimization of iron slab(110)

[rachita_panigrahi]

i am optimizing iron slab(110) suface in vasp having 234 atoms.. i have doubt on kpoints.can you just help me

[merzuk.kaltak]

A good choice for the KPOINTS file depends on the used POSCAR, specifically the length of the lattice vectors a,b,c defined in the POSCAR.
If N1, N2, N3 are the number of k-points in the first, second and third direction in the first Brillouin cell, like for instance in this KPOINTS file

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Gamma-centered KPOINTS
0
Gamma
N1 N2 N3

The I would set N1 and N2 and N3 such that N1 * a ~ N2 * b ~ N3 * c, where a, b, c is the length of the lattice vectors defined in the POSCAR.
If you have some tricky POSCAR it is helpful to visualize it in VESTA to find the lengths of the vectors.
For tight convergence you can multiply N1,N2,N3 with a common factor.
Here is an example of a POSCAR that is stretched

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Example cubic
1
4 0 0 
0 6 0
0 0 12

Since c is the largest vector set N3=1. Because a is 3 times smaller than c and b is in between a and b, I would use N1=3, N2=2.
If you use N3=2, then you should double N1 and N2 as well and use N1=6, N2=4 and so on.

[rachita_panigrahi]

here i am attaching the lattice vector

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 30.1232986450         0.0000000000         0.0000000000
        0.0000000000        30.1232986450         0.0000000000
        0.0000000000         0.0000000000        30.1232986450

and i am taking KPOINTS
1 1 1
is it correct?

[merzuk.kaltak]

The choice 111 seems reasonable.