Dear users, I am trying to achieve the perfect relaxation of hexagonal unit cell in orthorhombic coordinates, however, I still see quite substantial residual forces along z-dimension. Doing finer k-mesh sampling does not help with the issue. I am quite sure that the coordinates of atoms in each layer are correct, so I was expecting that vc-relax will result only in the change in the unit cell dimensions, but not the changes of atomic positions inside it.
Please, give me some hints of what could be wrong in my input to help me
achieve full relaxation of the unit cell.
Input (also attached):
&CONTROL
calculation = "vc-relax",
pseudo_dir = "/u/annakuz/espresso/pseudo",
outdir = "/lustre/work1/annakuz/tmp4",
/
&SYSTEM
ibrav = 8,
celldm(1) = 5.781869696282005, celldm(2) = 1.732050807568878,
celldm(3) = 1.632993161855452,
nat = 8,
ntyp = 2,
ecutwfc = 80,
ecutrho = 700,
occupations='smearing', smearing='gauss', degauss=0.03
/
&ELECTRONS
conv_thr = 1.D-12
/
&IONS
/
&CELL
/
ATOMIC_SPECIES
Si 28.0855 Si.pz-n-kjpaw_psl.0.1.UPF
C 12.0107 C.pz-n-kjpaw_psl.0.1.UPF
ATOMIC_POSITIONS {crystal}
Si 0.00 0.00 0.00
C 0.00 0.00 0.375
Si 0.50 0.50 0.00
C 0.50 0.50 0.375
Si 0.50 0.166666667 0.5
C 0.50 0.166666667 0.875
Si 1.00 0.666666667 0.5
C 1.00 0.666666667 0.875
K_POINTS automatic
15 8 9 1 1 1
Output is attached but here is the final result of relaxation showing
forces still present in z-direction:
............
convergence has been achieved in 31 iterations
Forces acting on atoms (Ry/au):
atom 1 type 1 force = 0.00000000 -0.00000037 0.00011491
atom 2 type 2 force = 0.00000000 0.00000026 -0.00011491
atom 3 type 1 force = 0.00000000 -0.00000037 0.00011493
atom 4 type 2 force = 0.00000000 0.00000030 -0.00011491
atom 5 type 1 force = 0.00000000 0.00000037 0.00011498
atom 6 type 2 force = 0.00000000 -0.00000029 -0.00011498
atom 7 type 1 force = 0.00000000 0.00000036 0.00011495
atom 8 type 2 force = 0.00000000 -0.00000027 -0.00011497
Total force = 0.000325 Total SCF correction = 0.000000
entering subroutine stress ...
total stress (Ry/bohr**3) (kbar) P=
-0.09
-0.00000088 0.00000000 0.00000000 -0.13 0.00 0.00
0.00000000 -0.00000088 0.00000000 0.00 -0.13 0.00
0.00000000 0.00000000 0.00000001 0.00 0.00 0.00
bfgs converged in 3 scf cycles and 2 bfgs steps
(criteria: energy < 0.10E-03, force < 0.10E-02, cell < 0.50E+00)
End of BFGS Geometry Optimization
Final enthalpy = -250.0275444323 Ry
Begin final coordinates
new unit-cell volume = 547.64431 a.u.^3 ( 81.15251 Ang^3 )
CELL_PARAMETERS (alat= 5.78186970)
0.998918439 0.000000000 0.000000000
0.000000000 1.730177232 0.000000000
0.000000000 0.000000000 1.639355189
ATOMIC_POSITIONS (crystal)
Si 0.000000000 -0.000000091 -0.000421399
C 0.000000000 -0.000000003 0.375421398
Si 0.500000000 0.499999909 -0.000421402
C 0.500000000 0.499999991 0.375421397
Si 0.500000000 0.166666758 0.499578593
C 0.500000000 0.166666675 0.875421409
Si 1.000000000 0.666666758 0.499578597
C 1.000000000 0.666666671 0.875421408
End final coordinates
Thank you for help!
--
Best regards,
Anna
2h_sic_pz_vcrelax5.rx.out
Description: Binary data
2h_sic_pz_vcrelax5.rx.in
Description: Binary data
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