<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">Dear all:<div class=""><br class=""><div class="">I am using pw.x and ph.x to calculate the dielectric constant of InAs, and here are some problems with the calculations.</div><div class=""><br class=""></div><div class="">(1) After structural relaxation using vc-relax, the stress is now zero (confirmed using scf calculations for the final structure). </div><div class=""><br class=""></div><div class=""><div class=""><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> convergence has been achieved in 10 iterations</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156); min-height: 18px;" class=""><br class=""></div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> Forces acting on atoms (Ry/au):</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156); min-height: 18px;" class=""><br class=""></div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> atom 1 type 1 force = 0.00000000 0.00000000 0.00000000</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> atom 2 type 2 force = 0.00000000 0.00000000 0.00000000</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156); min-height: 18px;" class=""><br class=""></div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> Total force = 0.000000 Total SCF correction = 0.000000</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156); min-height: 18px;" class=""><br class=""></div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156); min-height: 18px;" class=""><br class=""></div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> entering subroutine stress ...</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156); min-height: 18px;" class=""><br class=""></div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> total stress (Ry/bohr**3) (kbar) P= 0.00</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> 0.00000001 -0.00000000 -0.00000000 0.00 -0.00 -0.00</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> -0.00000000 0.00000001 0.00000000 -0.00 0.00 0.00</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> -0.00000000 0.00000000 0.00000001 -0.00 0.00 0.00</div></div></div><div class=""><br class=""></div><div class=""><br class=""></div><div class="">However, the following phonon calculation predicts not only negative phonon frequency at q = 0, but also very strange dielectric constant.</div><div class=""><br class=""></div><div class=""><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> Dielectric constant in cartesian axis </div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156); min-height: 18px;" class=""><br class=""></div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> ( -230.720680077 -0.000000000 0.000000000 )</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> ( -0.000000000 -230.720680077 0.000000000 )</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> ( 0.000000000 0.000000000 -230.720680077 )</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156); min-height: 18px;" class=""><br class=""></div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> Effective charges (d Force / dE) in cartesian axis</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156); min-height: 18px;" class=""><br class=""></div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> atom 1 In </div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> Ex ( 9.55076 0.00000 0.00000 )</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> Ey ( 0.00000 9.55076 0.00000 )</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> Ez ( 0.00000 0.00000 9.55076 )</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> atom 2 As </div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> Ex ( -9.43886 0.00000 0.00000 )</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> Ey ( -0.00000 -9.43886 -0.00000 )</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> Ez ( 0.00000 0.00000 -9.43886 )</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156); min-height: 18px;" class=""><br class=""></div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> Diagonalizing the dynamical matrix</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156); min-height: 18px;" class=""><br class=""></div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> q = ( 0.000000000 0.000000000 0.000000000 ) </div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156); min-height: 18px;" class=""><br class=""></div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> **************************************************************************</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> freq ( 1) = -6.064621 [THz] = -202.293974 [cm-1]</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> freq ( 2) = -6.064621 [THz] = -202.293974 [cm-1]</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> freq ( 3) = -6.064621 [THz] = -202.293974 [cm-1]</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> freq ( 4) = 0.164141 [THz] = 5.475159 [cm-1]</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> freq ( 5) = 0.164141 [THz] = 5.475159 [cm-1]</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> freq ( 6) = 0.164141 [THz] = 5.475159 [cm-1]</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> **************************************************************************</div></div><div class=""><br class=""></div><div class="">The input files are attached below for your reference. </div><div class=""><br class=""></div><div class="">(2) One more question, the vc-relax calculation converges at zero stress, which was calculated using the cut-off set for initial cell parameters, so one has to redo the calculations using the new cell parameters following the suggestion at <a href="http://www.quantum-espresso.org/faq/self-consistency/#6.11" class="">http://www.quantum-espresso.org/faq/self-consistency/#6.11</a>. Is there any better (more automatic) way to obtain a final relaxed cell/atom structures?</div><div class=""><br class=""></div><div class="">Could any one help me on these two questions?</div><div class=""><br class=""></div><div class="">Thank you,</div><div class=""><br class=""></div><div class="">Zhiping</div></div><div class=""><br class=""></div><div class="">input files:</div><div class=""><br class=""></div><div class="">—scf.in—</div><div class=""><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class="">&control</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> calculation = 'scf',</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> restart_mode = 'from_scratch',</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> pseudo_dir = '/home/xuzp/bin/lib/upf_files',</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> outdir = '.',</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> prefix = 'InAs',</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> tstress = .true.</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> tprnfor = .true.</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> wf_collect = .true.</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class="">/</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class="">&system</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> ibrav = 2, </div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> celldm(1) = 11.69675,</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> nat = 2, </div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> ntyp = 2,</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> ecutwfc = 90,<span class="Apple-tab-span" style="white-space: pre;"> </span></div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class="">/</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class="">&electrons</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> diagonalization = 'cg'</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> conv_thr = 1.0d-10</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class="">/</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156); min-height: 18px;" class=""><br class=""></div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class="">ATOMIC_SPECIES</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> In 111.818 In.pbe-dn-rrkjus_psl.0.2.2.UPF</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> As 74.920 As.pbe-n-rrkjus_psl.0.2.UPF</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156); min-height: 18px;" class=""><br class=""></div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class="">ATOMIC_POSITIONS crystal</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> In 0.00 0.00 0.00</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> As 0.25 0.25 0.25</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156); min-height: 18px;" class=""><br class=""></div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class="">K_POINTS automatic </div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> 9 9 9 0 0 0 </div></div><div class=""><br class=""></div><div class="">—ph.in—</div><div class=""><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class="">phonons of InAs</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class="">&inputph</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> tr2_ph = 1.0d-16,</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> niter_ph = 100,</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> prefix = 'InAs',</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> epsil = .true.<span class="Apple-tab-span" style="white-space:pre"> </span> </div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> amass(1) = 111.818,</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> amass(2) = 74.920,</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> outdir = '.',</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class=""> fildyn = 'InAs.matdyn',</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class="">/</div><div style="margin: 0px; font-family: Menlo; background-color: rgb(254, 244, 156);" class="">0.0 0.0 0.0</div></div></body></html>