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<br><font size="3">Dear all</font><div><font size="3"><br></font></div><div><font size="3">I want to perform a vc-relax calculation for NbSi2 :</font></div><div><font size="3"><br></font></div><div><font size="3">First i use the following input : </font><br><div><br></div></div><div><span style="font-family: 'lucida grande', tahoma, verdana, arial, sans-serif; font-size: 11px; line-height: 14px; text-align: left; background-color: rgb(255, 255, 255); ">ý&CONTROL</span><br style="font-family: 'lucida grande', tahoma, verdana, arial, sans-serif; font-size: 11px; line-height: 14px; text-align: left; background-color: rgb(255, 255, 255); "><span style="font-family: 'lucida grande', tahoma, verdana, arial, sans-serif; font-size: 11px; line-height: 14px; text-align: left; background-color: rgb(255, 255, 255); ">title = 'NbSi2',</span><br style="font-family: 'lucida grande', tahoma, verdana, arial, sans-serif; font-size: 11px; line-height: 14px; text-align: left; background-color: rgb(255, 255, 255); "><span style="font-family: 'lucida grande', tahoma, verdana, arial, sans-serif; font-size: 11px; line-height: 14px; text-align: left; background-color: rgb(255, 255, 255); ">calculation = 'vc-relax',</span><br style="font-family: 'lucida grande', tahoma, verdana, arial, sans-serif; font-size: 11px; line-height: 14px; text-align: left; background-color: rgb(255, 255, 255); "><span style="font-family: 'lucida grande', tahoma, verdana, arial, sans-serif; font-size: 11px; line-height: 14px; text-align: left; background-color: rgb(255, 255, 255); ">nstep = 100,</span><br style="font-family: 'lucida grande', tahoma, verdana, arial, sans-serif; font-size: 11px; line-height: 14px; text-align: left; background-color: rgb(255, 255, 255); "><span style="font-family: 'lucida grande', tahoma, verdana, arial, sans-serif; font-size: 11px; line-height: 14px; text-align: left; background-color: rgb(255, 255, 255); ">etot_conv_thr = 1.d-7,</span><br style="font-family: 'lucida grande', tahoma, verdana, arial, sans-serif; font-size: 11px; line-height: 14px; text-align: left; background-color: rgb(255, 255, 255); "><span class="text_exposed_show" style="display: inline; font-family: 'lucida grande', tahoma, verdana, arial, sans-serif; font-size: 11px; line-height: 14px; text-align: left; background-color: rgb(255, 255, 255); ">forc_conv_thr = 1.d-5,<br>tstress = .true.,<br>prefix = 'NbSi2',<br>verbosity = 'high',<br>disk_io = 'low',<br>tprnfor = .true.,<br>/<br>&SYSTEM<br>celldm(1) = 1.d0,<br>ibrav = 0, <br>nat = 9,<br>ntyp = 2,<br>ecutwfc = 30.d0,<br>ecutrho = 300.d0,<br>nspin = 1,<br>occupations = 'smearing',</span></div><div><span class="text_exposed_show" style="display: inline; font-family: 'lucida grande', tahoma, verdana, arial, sans-serif; font-size: 11px; line-height: 14px; text-align: left; background-color: rgb(255, 255, 255); ">degauss = 0.005d0,<br>/<br>&ELECTRONS<br>conv_thr = 1.d-7,<br>mixing_beta = 0.1d0,<br>diagonalization = 'cg',<br>/<br>&IONS<br>ion_dynamics = 'bfgs',<br>bfgs_ndim = 1,<br>/<br>&CELL<br>cell_dynamics = 'bfgs',<br>press = 0.d0,<br>press_conv_thr = 0.200d0,<br>cell_dofree = 'xyz',<br>/<br>ATOMIC_SPECIES<br>Si 28.0855d0 Si.pbe-n-van.UPF<br>Nb 92.90638d0 Nb.pbe-nsp-van.UPF<br><br>K_POINTS automatic<br>6 6 1 0 0 0<br><br>ATOMIC_POSITIONS crystal<br>Nb 0.50000 0.00000 0.00000 <br>Si 0.16578 0.33156 0.00000<br>Nb 0.00000 0.50000 0.66667 <br>Si 0.66844 0.83422 0.66667 <br>Nb 0.50000 0.50000 0.33333 <br>Si 0.16578 0.83422 0.33333 <br>Si 0.83422 0.66844 0.00000 <br>Si 0.33156 0.16578 0.66667 <br>Si 0.83422 0.16578 0.33333 <br><br>CELL_PARAMETERS<br>9.053677211 0.000000000 0.000000000<br>0.000000000 9.053677211 0.000000000<br>0.000000000 0.000000000 12.449514813</span>
</div><div><span class="text_exposed_show" style="display: inline; font-family: 'lucida grande', tahoma, verdana, arial, sans-serif; font-size: 11px; line-height: 14px; text-align: left; background-color: rgb(255, 255, 255); "><br></span></div><div><span class="text_exposed_show" style="display: inline; font-family: 'lucida grande', tahoma, verdana, arial, sans-serif; font-size: 11px; line-height: 14px; text-align: left; background-color: rgb(255, 255, 255); "><br></span></div><div style="text-align: left;"><font size="3"><font face="'lucida grande', tahoma, verdana, arial, sans-serif"><span style="line-height: 14px;">During convergence, the error was : </span></font>Not enough space allocated for radial FFT: try restarting with a larger cell_factor</font></div><div style="text-align: left;"><font size="3"><br></font></div><div style="text-align: left;"><font size="3">So, i use a cell_factor = 2 , then the structure was converged, but the cell parameters of the relaxed structure differs so much from the cell-parameters of the begining.</font></div><div style="text-align: left;"><font size="3"><br></font></div><div style="text-align: left;"><font size="3">relaxed cell parameters :</font></div><div style="text-align: left;"><font size="3"><span style="font-family: 'lucida grande', tahoma, verdana, arial, sans-serif; line-height: 14px; background-color: rgb(255, 255, 255); ">10.94171211 0.000000000 0.000000000</span></font></div><div style="text-align: left;"><font size="3"><br style="font-family: 'lucida grande', tahoma, verdana, arial, sans-serif; line-height: 14px; "><span style="font-family: 'lucida grande', tahoma, verdana, arial, sans-serif; line-height: 14px; background-color: rgb(255, 255, 255); ">0.000000000 10.94171211 0.000000000</span></font></div><div style="text-align: left;"><font size="3"><br style="font-family: 'lucida grande', tahoma, verdana, arial, sans-serif; line-height: 14px; "><span style="font-family: 'lucida grande', tahoma, verdana, arial, sans-serif; line-height: 14px; background-color: rgb(255, 255, 255); ">0.000000000 0.000000000 9.245414256</span></font></div><div style="text-align: left;"><span style="font-size: 10pt; "><br></span></div><div style="text-align: left;"><font size="3">I try to decrease ecutwfc for 25 Ry and ecutrho = 200 Ry, and to change the 'smearing' , but always i converge the structure with a big difference between cell_parameters.</font></div><div style="text-align: left;"><font size="3">the difference between cell-parameters is about 20%.</font></div><div style="text-align: left;"><font size="3"><br></font></div><div style="text-align: left;"><font size="3">So my question is : What is the real problem in my input ?</font></div><div style="text-align: left;"><font size="3"><br></font></div><div style="text-align: left;"><font size="3">Thanks a lot for your helping </font></div><div style="text-align: left;"><font size="3"><br></font></div><div style="text-align: left;"><font size="3">best regards</font></div><div style="text-align: left;"><font size="3"><br></font></div><div style="text-align: left;"><font size="3">Ali ALLAM</font></div><div style="text-align: left;"><font size="3">Physics of materials - 2nd year PhD</font></div><div style="text-align: left;"><font size="3">Aix-Marseille University</font></div><div style="text-align: left;"><font size="3">Marseille 13013</font></div><div style="text-align: left;"><font size="3">FRANCE</font></div><pre><br></pre> </div></body>
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