<div dir="ltr"><div>Dear users,</div><div><br></div><div>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. </div><div>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.</div><div><br></div><div>Please, give me some hints of what could be wrong in my input to help me achieve full relaxation of the unit cell. </div><div><br></div><div><br></div><div>Input (also attached):</div><div><br></div><div>&CONTROL<br> calculation = "vc-relax",<br> pseudo_dir = "/u/annakuz/espresso/pseudo",<br> outdir = "/lustre/work1/annakuz/tmp4",<br>/<br>&SYSTEM<br> ibrav = 8,<br> celldm(1) = 5.781869696282005, celldm(2) = 1.732050807568878, celldm(3) = 1.632993161855452,<br> nat = 8,<br> ntyp = 2,<br> ecutwfc = 80,<br> ecutrho = 700,<br> occupations='smearing', smearing='gauss', degauss=0.03<br>/<br>&ELECTRONS<br> conv_thr = 1.D-12<br>/<br>&IONS<br>/<br>&CELL<br>/<br>ATOMIC_SPECIES<br>Si 28.0855 Si.pz-n-kjpaw_psl.0.1.UPF<br>C 12.0107 C.pz-n-kjpaw_psl.0.1.UPF<br>ATOMIC_POSITIONS {crystal}<br>Si 0.00 0.00 0.00<br>C 0.00 0.00 0.375<br>Si 0.50 0.50 0.00<br>C 0.50 0.50 0.375</div><div>Si 0.50 0.166666667 0.5<br>C 0.50 0.166666667 0.875<br>Si 1.00 0.666666667 0.5<br>C 1.00 0.666666667 0.875</div><div><br></div><div>K_POINTS automatic<br>15 8 9 1 1 1<br></div><div><br></div><div><br></div><div>Output is attached but here is the final result of relaxation showing forces still present in z-direction:</div><div><br></div><div>............</div><div> convergence has been achieved in 31 iterations</div><div> Forces acting on atoms (Ry/au):</div><div> atom 1 type 1 force = 0.00000000 -0.00000037 0.00011491<br> atom 2 type 2 force = 0.00000000 0.00000026 -0.00011491<br> atom 3 type 1 force = 0.00000000 -0.00000037 0.00011493<br> atom 4 type 2 force = 0.00000000 0.00000030 -0.00011491<br> atom 5 type 1 force = 0.00000000 0.00000037 0.00011498<br> atom 6 type 2 force = 0.00000000 -0.00000029 -0.00011498<br> atom 7 type 1 force = 0.00000000 0.00000036 0.00011495<br> atom 8 type 2 force = 0.00000000 -0.00000027 -0.00011497</div><div> Total force = 0.000325 Total SCF correction = 0.000000</div><div><br> entering subroutine stress ...</div><div> total stress (Ry/bohr**3) (kbar) P= -0.09<br> -0.00000088 0.00000000 0.00000000 -0.13 0.00 0.00<br> 0.00000000 -0.00000088 0.00000000 0.00 -0.13 0.00<br> 0.00000000 0.00000000 0.00000001 0.00 0.00 0.00</div><div><br> bfgs converged in 3 scf cycles and 2 bfgs steps<br> (criteria: energy < 0.10E-03, force < 0.10E-02, cell < 0.50E+00)</div><div> End of BFGS Geometry Optimization</div><div> Final enthalpy = -250.0275444323 Ry<br>Begin final coordinates<br> new unit-cell volume = 547.64431 a.u.^3 ( 81.15251 Ang^3 )</div><div><br></div><div>CELL_PARAMETERS (alat= 5.78186970)<br> 0.998918439 0.000000000 0.000000000<br> 0.000000000 1.730177232 0.000000000<br> 0.000000000 0.000000000 1.639355189</div><div>ATOMIC_POSITIONS (crystal)<br>Si 0.000000000 -0.000000091 -0.000421399<br>C 0.000000000 -0.000000003 0.375421398<br>Si 0.500000000 0.499999909 -0.000421402<br>C 0.500000000 0.499999991 0.375421397<br>Si 0.500000000 0.166666758 0.499578593<br>C 0.500000000 0.166666675 0.875421409<br>Si 1.000000000 0.666666758 0.499578597<br>C 1.000000000 0.666666671 0.875421408<br>End final coordinates<br><br></div><div> Thank you for help!<br>-- <br></div><div class="gmail_signature">Best regards,<br>Anna</div>
</div>