<div dir="ltr"><div>These are the only symmetries that are detected in your input, and the only ones that are conserved during the relaxation:<br><br> 2 Sym. Ops. (no inversion) found<br><br><br> s frac. trans.<br><br> isym = 1 identity <br><br> cryst. s( 1) = ( 1 0 0 )<br> ( 0 1 0 )<br> ( 0 0 1 )<br><br> cart. s( 1) = ( 1.0000000 0.0000000 0.0000000 )<br> ( 0.0000000 1.0000000 0.0000000 )<br> ( 0.0000000 0.0000000 1.0000000 )<br><br><br> isym = 2 inv. 180 deg rotation - cart. axis [0,0,1] <br><br> cryst. s( 2) = ( 0 0 1 )<br> ( 0 1 0 )<br> ( 1 0 0 )<br><br> cart. s( 2) = ( 1.0000000 0.0000000 0.0000000 )<br> ( 0.0000000 1.0000000 0.0000000 )<br> ( 0.0000000 0.0000000 -1.0000000 )<br><br><br> point group C_s (m) <br> there are 2 classes<br> the character table:<br><br> E s <br>A' 1.00 1.00<br>A'' 1.00 -1.00<br><br> the symmetry operations in each class and the name of the first element:<br><br> E 1<br> identity <br> s 2<br> inv. 180 deg rotation - cart. axis [0,0,1] <br><br></div>Paolo<br></div><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Oct 3, 2017 at 8:32 AM, JAY Antoine <span dir="ltr"><<a href="mailto:Antoine.JAY@isae-supaero.fr" target="_blank">Antoine.JAY@isae-supaero.fr</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">If symmetries are conserved, why do I obtained non zero terms in the CELL_PARAMETERS where there should be zero terms?<br>Here is a full example in which i asked for relaxation of a monoclinic base-center system with cell parameters<br>v1 = ( a/2, 0, -c/2),<br>v2 = (b*cos(gamma), b*sin(gamma), 0),<br>v3 = ( a/2, 0, c/2)<br>but in the output v1(2) and v3(2) are not exactelly null!!<br>To obtain the celldm, if I use the reversed equations<br>celldm(2)=b/a<br>celldm(3)=c/a,<br>celldm(4)=cos(ab)<br>I do not take into account these non zero values, which then gives the wrong atomic positions.<br>Fortunatelly, the loose of symmetry is small, and if use these "wrong" celldm in a second vc-relax, then third and fourth,<br>until the relaxation becomes useless, I finally obtain v1(2) and v3(2) exactelly null so the reversed equations gives the right celldm.<br>But this is not the good way to do it as one vc-relax that concerve the symmetries the should be the good way.<br><br>My input/output example:<br>as input: <br>&system<br> ibrav = 13,<br> celldm(1) = 16.288976472<br> celldm(2) = 0.544519937<br> celldm(3) = 0.668172534<br> celldm(4) = 0.501142811<br> nat= 13,<br> ntyp= 2, <br> ecutwfc =80,<br> occupations='smearing',<br> smearing='mp',<br> degauss=0.0015,<br>/<br> &electrons<br> diagonalization='david'<br> mixing_beta = 0.7<br> conv_thr = 4.0d-13<br> electron_maxstep=800<br>/<br>&ions<br> ion_dynamics='damp'<br> pot_extrapolation='second_<wbr>order'<br> wfc_extrapolation='second_<wbr>order'<br> /<br>&CELL<br> cell_dynamics='bfgs',<br> press = 0,<br> press_conv_thr=0.1D0<br> cell_factor=2<br>ATOMIC_SPECIES<br>B 10.810 B-EB.pw<br>C 12.011 C-EB.pw<br>ATOMIC_POSITIONS {crystal}<br>B -0.188793817 -0.218234974 0.307727082<br>B -0.192719364 0.340793252 -0.192719364<br>B 0.307727082 -0.218234974 -0.188793817<br>B 0.190169938 0.219331860 -0.303953219<br>B 0.194974825 -0.339438271 0.194974825<br>B -0.303953219 0.219331860 0.190169938<br>B 0.007880732 -0.005471582 0.338682645<br>B 0.010098557 0.335888236 0.010098557<br>B 0.338682645 -0.005471582 0.007880732<br>B -0.005624351 0.003265079 -0.333219342<br>C -0.003954045 -0.319654369 -0.003954045<br>B -0.333219342 0.003265079 -0.005624351<br>C 0.425826764 0.426219771 0.425826764<br>K_POINTS {automatic}<br>12 12 12 1 1 1<br><br>as output:<br>CELL_PARAMETERS (alat= 16.28897647)<br> 0.498490550 0.013603023 -0.308425490<br> 0.284663797 0.492181426 -0.000000000<br> 0.498490550 0.013603023 0.308425490<br>ATOMIC_POSITIONS (crystal)<br>B -0.202019099 -0.212621756 0.346315439<br>B -0.205370945 0.354119566 -0.205370945<br>B 0.346315439 -0.212621756 -0.202019099<br>B 0.206012998 0.209180405 -0.314139284<br>B 0.204538774 -0.320989968 0.204538774<br>B -0.314139284 0.209180405 0.206012998<br>B 0.005743670 0.002927514 0.339636302<br>B 0.004144354 0.351749983 0.004144354<br>B 0.339636302 0.002927514 0.005743670<br>B 0.006794941 -0.000361453 -0.329132341<br>C 0.002164917 -0.321786041 0.002164917<br>B -0.329132341 -0.000361453 0.006794941<br>C 0.382406681 0.380246423 0.382406681<br><br>Best regards,<br>Antoine Jay<br><br><br><br><br><br>On Monday, October 02, 2017 21:43 CEST, Paolo Giannozzi <<a href="mailto:p.giannozzi@gmail.com" target="_blank">p.giannozzi@gmail.com</a>> wrote:<br> <blockquote type="cite" cite="http://CAPMgbCt9+hRqbVBfAep6i4FbABwffN3eo=mBPh2XWJby3pSV=A@mail.gmail.com"><div dir="ltr">On Mon, Oct 2, 2017 at 4:25 PM, JAY Antoine <span dir="ltr"><<a href="mailto:Antoine.JAY@isae-supaero.fr" target="_blank">Antoine.JAY@isae-supaero.fr</a>></span> wrote:<div class="gmail_extra"><div class="gmail_quote"><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><span>I would like to perform a vc-relax that conserves the point group of each atom and the symmetry of the cell.</span></blockquote><div> </div><div>vc-relax conserves the starting symmetry of the crystal. There is no way to conserve a symmetry that is not there at the beginning of the structural optimization.<br> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><span>For example, in a trigonal cell, ibrav 5 imposes the symmetries:<br>v1 = a(tx,-ty,tz)<br>v2 = a(0,2ty,tz)<br>v3 = a(-tx,-ty,tz)<br>but these symmetries seem to be broken by the relaxation,</span></blockquote><div> </div><div>see above: symmetries that were present in the starting structure are not broken. If a "symmetry" is "broken by structural relaxation", it wasn't a symmetry.<br> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><span>so that at the end of the relaxation, v2(1) is not exactly null and v1(1) is not exactly -v3(1),</span><br>or for the atomic positions, a coordinate (x, x, x) alat becomes (x, 0.99 x, 1.001x ).<div class="m_4780517040263026047HOEnZb"><div class="m_4780517040263026047h5"><br><br>?? Is it possible to impose that these constraints on the unit-cell and on the atomic positions stay fix during the relaxation process ??<br><br>This is a major issue for the use of these relaxed values in a second step for phonons for example, because it will then not detect the symmetries.<br>I think it could be a good idea to add into the vc-relax output file a lign that gives the corresponding celldm(i) and not only the CELL_PARAMETERS.</div></div></blockquote><div> </div><div>I also think that it is a good idea, but it takes a bit of time and effort, that becomes a byte, or even a word (32 or 64 bits) if one wants to write a piece of code that works perfectly in all cases<br> </div><div>Paolo</div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="m_4780517040263026047HOEnZb"><div class="m_4780517040263026047h5">In fact, in the scf before the phonon use, we would like to have ibrav =/0 and celldm in state of ibrav 0 and quasi symmetric CELL_PARAMETERS...<br><br>Best regards,<br><br>Antoine Jay<br> </div></div></blockquote></div><br clear="all"><br>--<div class="m_4780517040263026047gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div>Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,<br>Univ. Udine, via delle Scienze 208, 33100 Udine, Italy<br>Phone <a href="tel:+39%200432%20558216" value="+390432558216" target="_blank">+39-0432-558216</a>, fax <a href="tel:+39%200432%20558222" value="+390432558222" target="_blank">+39-0432-558222</a><br> </div></div></div></div></div></div></div></blockquote><br><br><br>
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