Dear Sai Varun Ragi
I've read your input and opened your structure with xcrysden and I can
give you some suggestions:
1) When I simulate the interaction of a molecule with a surface I do as
follows:
a) a "vc-relax" calculations of the BULK unit cell with converged
parameters (wfc, rho, k-points, you can find many tutorials to calculate
them).
b) a "relax" calculations of a surface slab, using adequate vacuum
between periodically repeated images.
c) one or many "relax" calculations to find the most stable adsorption
geometry of the molecule on the surface
Thus first of all optimize the surface slab, this can improve the
stability of your molecule-surface calculation.
2) You can place the molecules above and below the slab in symmetrical
positions, but in my opinion this is not satisfactory as it increases
without reasons the number of electrons of the system. You may use one
of the several available dipole corrections or open-boundary conditions
along the z axis, I generally use ESM in a vacuum-slab-vacuum
configuration (read pw.x manual, please).
assume_isolated = 'esm',
esm_bc='bc1',
3) You have fully saturated the surface with one O2 molecule per surface
unit cell (coverage = 1). Is this what you want to simulate? Is this a
realistic physical description of your system or you need to perform a
calculation using a larger surface supercell with only one O2 molecule
isolated from the interaction with neighboring molecules?
4) Don't use nband when you use smearing, pw.x add enough empty states
to ensure convergence of metals or semiconductors.
5) paramagnetic systems are activated by nspin=2. However, you don't
need to provide starting magnetization for Ti and C in the case of a
surface slab without O molecules.
6) In case of further difficulties in scf convergence with many " too
many bands have not converged " errors, you can reduce mixing_beta down
to even 0.01 and you may also try with this diagonalization scheme
diagonalization='ppcg',
diago_thr_init=1.0d-7
HTH
Giuseppe
Il 2026-01-31 14:21 SAI VARUN RAGI . ha scritto:
Hello all,
I am doing vc-relax for the unit cell Ti3C2O2 but everytime it's
failing or it's telling maximum time reached and some other statements
like " too many bands have not converged " or "cannot bracket Ef".
What I did is I have taken Ti3C2 from the materials library and just
kept the O2 molecule on the top and below the unit cell nearly 3-5
Angstrom awy such that there is no bond.
I have tried the same for other Ti3C2T2 too and getting near the same
results.
Below is the input code. I have even tried cg and paro diagonalization
too but it fails and the iteration stops suddenly without crashing.
Could you please tell me what to do?
&CONTROL
calculation = "vc-relax"
forc_conv_thr = 1.00000e-03
max_seconds = 1.72800e+05
nstep = 300
pseudo_dir = "../pseudo/"
/
&SYSTEM
a = 3.06660e+00
c = 5.22788e+01
degauss = 1.00000e-02
ecutrho = 5.00000e+02
ecutwfc = 7.00000e+01
ibrav = 4
nat = 14
nspin = 1
ntyp = 3
nbnd = 100
occupations = "smearing"
smearing = "gaussian"
starting_magnetization(1) = 0.00000e+00
starting_magnetization(2) = 0.00000e+00
starting_magnetization(3) = 2.00000e-01
/
&ELECTRONS
diagonalization = 'david'
conv_thr = 1.00000e-08
electron_maxstep = 300
mixing_mode = "plain"
mixing_beta = 4.00000e-01
startingpot = "atomic"
startingwfc = "atomic+random"
/
&IONS
ion_dynamics = "bfgs"
/
&CELL
cell_dynamics = "bfgs"
press_conv_thr = 5.00000e-01
/
K_POINTS {automatic}
5 5 1 0 0 0
ATOMIC_SPECIES
Ti 47.86700 Ti.pbe-spn-kjpaw_psl.1.0.0.UPF.txt
C 12.01070 C.pbe-n-kjpaw_psl.1.0.0.UPF.txt
O 15.99940 O.pbe-n-kjpaw_psl.1.0.0.UPF.txt
ATOMIC_POSITIONS {angstrom}
Ti 0.000000 1.770505 32.278823
C 1.533303 0.885253 31.217205
Ti 0.000000 0.000000 29.918699
C 0.000000 1.770505 28.620193
Ti 1.533303 0.885253 27.558575
Ti 1.533303 0.885253 24.720248 0 0 0
C 0.000000 1.770505 23.658630 0 0 0
Ti 0.000000 0.000000 22.360124 0 0 0
C 1.533303 0.885253 21.061618 0 0 0
Ti 0.000000 1.770505 20.000000 0 0 0
O 1.489621 0.925290 33.965155
O 0.814054 1.114514 34.393699
O 0.561620 0.758451 17.829438
O 1.494167 1.296806 18.121178
Many Thanks,
Sai Varun Ragi
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