<div dir="ltr">Dear All,<div><br></div><div>I have been trying to optimize the structure of single layer hexagonal BNC. The vc-relax run finished smoothly and gave me the optimized positions of each atom and the lattice parameters. </div><div><br></div><div>However, if I use these optimized values for scf calculation, it gave me large force between atom and large stress. If I use these values for another vc-relax run, then it will take quite a few bfgs steps to get the optimized atomic positions and lattice parameters. Surprisingly, they are different from the values I got from the last vc-relax run. </div><div><br></div><div>Could you please help me with this? My code is pasted below.</div><div><br></div><div>Thanks,</div><div>Lei </div><div> </div><div>------------------<br clear="all"><div>







<p class="gmail-p1"><span class="gmail-s1"> &control</span></p>
<p class="gmail-p1"><span class="gmail-s1">    calculation = 'vc-relax'</span></p>
<p class="gmail-p1"><span class="gmail-s1">    restart_mode='from_scratch',</span></p>
<p class="gmail-p1"><span class="gmail-s1">    prefix='BNC',</span></p>
<p class="gmail-p1"><span class="gmail-s1">    tstress = .true.</span></p>
<p class="gmail-p1"><span class="gmail-s1">    tprnfor = .true.</span></p>
<p class="gmail-p1"><span class="gmail-s1">    pseudo_dir = '/home/QE/pseudo/',</span></p>
<p class="gmail-p1"><span class="gmail-s1">    outdir='./temp_dir/'</span></p>
<p class="gmail-p1"> /<br></p>
<p class="gmail-p1"><span class="gmail-s1"> &system</span></p>
<p class="gmail-p1"><span class="gmail-s1">    ibrav=  4, celldm(1)= 9.53616076609, celldm(3) = 3.99905580615, nat= 8, ntyp= 3,</span></p>
<p class="gmail-p1"><span class="gmail-s1">    ecutwfc = 120.0</span></p>
<p class="gmail-p1"><span class="gmail-s1">    occupations='smearing', smearing = 'mv', degauss = 0.002</span></p>
<p class="gmail-p1"><span class="gmail-s1"> /</span></p>
<p class="gmail-p1"><span class="gmail-s1"> &electrons</span></p>
<p class="gmail-p1"><span class="gmail-s1">    diagonalization='david'</span></p>
<p class="gmail-p1"><span class="gmail-s1">    mixing_mode = 'plain'</span></p>
<p class="gmail-p1"><span class="gmail-s1">    mixing_beta = 0.7</span></p>
<p class="gmail-p1"><span class="gmail-s1">    conv_thr =  1.d-13,</span></p>
<p class="gmail-p1"><span class="gmail-s1"> /</span></p>
<p class="gmail-p1"><span class="gmail-s1"> &IONS</span></p>
<p class="gmail-p1"><span class="gmail-s1"> /</span></p>
<p class="gmail-p1"><span class="gmail-s1"> &CELL</span></p>
<p class="gmail-p1"><span class="gmail-s1">    cell_dynamics = 'bfgs' ,</span></p>
<p class="gmail-p1"><span class="gmail-s1">    press = 0.00,</span></p>
<p class="gmail-p1"><span class="gmail-s1">    wmass =  0.00700000,</span></p>
<p class="gmail-p1"><span class="gmail-s1">    press_conv_thr = 0.1,</span></p>
<p class="gmail-p1"><span class="gmail-s1">    cell_dofree = '2Dxy'</span></p>
<p class="gmail-p1"><span class="gmail-s1"> /  </span></p>
<p class="gmail-p1"><span class="gmail-s1">ATOMIC_SPECIES</span></p>
<p class="gmail-p1"><span class="gmail-s1"> B   10.811     B.pbe-mt_fhi.UPF</span></p>
<p class="gmail-p1"><span class="gmail-s1"> N   14.00674   N.pbe-mt_fhi.UPF</span></p>
<p class="gmail-p1"><span class="gmail-s1"> C   12.0107   C.pbe-mt_fhi.UPF</span></p>
<p class="gmail-p1"><span class="gmail-s1">ATOMIC_POSITIONS crystal</span></p>
<p class="gmail-p1"><span class="gmail-s1">B        0.002466254   0.004932509  -0.000000000</span></p>
<p class="gmail-p1"><span class="gmail-s1">N        0.170582689   0.341165379  -0.000000000</span></p>
<p class="gmail-p1"><span class="gmail-s1">N        0.496083977  -0.007832045  -0.000000000</span></p>
<p class="gmail-p1"><span class="gmail-s1">B        0.664200413   0.328400824   0.000000000</span></p>
<p class="gmail-p1"><span class="gmail-s1">C        0.013913144   0.504233187   0.000000000</span></p>
<p class="gmail-p1"><span class="gmail-s1">C        0.176346623   0.829100147  -0.000000000</span></p>
<p class="gmail-p1"><span class="gmail-s1">C        0.490320044   0.504233187   0.000000000</span></p>
<p class="gmail-p1"><span class="gmail-s1">C        0.652753523   0.829100147   0.000000000</span></p>
<p class="gmail-p1"><span class="gmail-s1">K_POINTS automatic</span></p>
<p class="gmail-p1"><span class="gmail-s1"> 16 16 1 0 0 0</span></p></div>
</div></div>