<html><head></head><body><div class="ydp947a4f7eyahoo-style-wrap" style="font-family: Helvetica Neue, Helvetica, Arial, sans-serif; font-size: 16px;"><div dir="ltr" data-setdir="false" style="font-size: 16px;">Hello!</div><div dir="ltr" data-setdir="false" style="font-size: 16px;"><br></div><div dir="ltr" data-setdir="false" style="">Please help with the following. <span style="font-size: medium;">I got the result of calculating the elastic constants of LKBO (orthorhombic, P212121, Space group 19) using thermo_pw (what='scf_elastic_constants', 'elastic algorithm = 'advanced'). The calculation was done, but I found 2 problems:</span></div><div dir="ltr" data-setdir="false" style=""><font size="3"><br></font><div style=""><div style=""><font size="3">1) the resulting matrix is asymmetric:</font></div><div style="" dir="ltr" data-setdir="false"><font size="3"><div><div><span style="font-size: 13px;"> 0.1310416661E+04 0.5760227795E+03 0.3377111274E+03 0 0 0</span></div><div><span style="font-size: 13px;"> 0.5721874370E+03 0.7221687324E+03 0.3757178266E+03 0 0 0</span></div><div><span style="font-size: 13px;"> 0.3222687958E+03 0.3774439747E+03 0.1122193660E+04 0 0 0</span></div><div><span style="font-size: 13px;"> 0 0 0 0.2688418051E+03 0 0 </span></div><div><span style="font-size: 13px;"> 0 0 0 0 0.2782351915E+03 0 </span></div><div><span style="font-size: 13px;"> 0 0 0 0 0 0.2810735472E+03</span></div></div><br></font></div><div style=""><font size="3"><br></font></div><div style="" dir="ltr" data-setdir="false"><span style="font-size: medium;">2) the data do not correspond to experimental results.</span><br></div><div style="font-size: 16px;"><span style="font-size: 13px;"><br></span></div><div style=""><font size="3">Some explanations:</font></div><div style="" dir="ltr" data-setdir="false"><font size="3">I noticed that in half SCF calculations, QE identified the symmetry of the crystal as monoclinic (<span><span style="font-size: 13px;">bravais-lattice index = 12 or -12</span></span>), and in the others - </font><span style="font-size: 13px;">bravais-lattice index = 8 (</span><span style="font-size: medium;">orthorhombic). At the start, we received the following symmetry information:</span><font size="3"><div><div><br></div><div dir="ltr" data-setdir="false"><div><div><span style="font-size: 13px;"> Bravais lattice 8 simple orthorhombic </span></div><div><span style="font-size: 13px;"> Point group number 8 / 38 D_2 (222)</span></div><div><span style="font-size: 13px;"><br></span></div><div><span style="font-size: 13px;"> The coset representatives of the space group with</span></div><div><span style="font-size: 13px;"> the standard order of operations are:</span></div><div><span style="font-size: 13px;"><br></span></div><div><span style="font-size: 13px;"> Fractional translations in crystal coordinates</span></div><div><span style="font-size: 13px;"><br></span></div><div><span style="font-size: 13px;"> PGS Fract. transl. (all) Fract. transl. (no shift) SGS</span></div><div><span style="font-size: 13px;"><br></span></div><div><span style="font-size: 13px;"> E 1 -0.0000 -0.0000 -0.0000 0.0000 0.0000 0.0000 E 1</span></div><div><span style="font-size: 13px;"> 2z 2 -0.5000 -0.0000 0.5000 0.0000 0.0000 0.5000 2z1 65</span></div><div><span style="font-size: 13px;"> 2x 4 0.5000 -0.5000 -0.0000 0.5000 0.0000 0.0000 2x1 67</span></div><div><span style="font-size: 13px;"> 2y 3 -0.0000 0.5000 -0.5000 0.0000 0.5000 0.0000 2y1 66</span></div><div><span style="font-size: 13px;"><br></span></div><div><span style="font-size: 13px;"> PGS = Point group symmetry, SGS = space group symmetry </span></div><div><span style="font-size: 13px;"> (no shift) means the part of the fractional translation</span></div><div><span style="font-size: 13px;"> that cannot be removed by an origin shift</span></div><div><span style="font-size: 13px;"><br></span></div><div><span style="font-size: 13px;"> Fractional translation shift and origin shift in crystal coordinates</span></div><div><span style="font-size: 13px;"><br></span></div><div><span style="font-size: 13px;"> PGS FT shift &Origin shift SGS</span></div><div><span style="font-size: 13px;"><br></span></div><div><span style="font-size: 13px;"> E 1 -0.0000 -0.0000 -0.0000 0.0000 0.0000 0.0000 E 1</span></div><div><span style="font-size: 13px;"> 2z 2 -0.5000 0.0000 0.0000 -0.2500 0.0000 0.0000 2z1 65</span></div><div><span style="font-size: 13px;"> 2x 4 0.0000 -0.5000 0.0000 0.0000 -0.2500 0.0000 2x1 67</span></div><div><span style="font-size: 13px;"> 2y 3 0.0000 0.0000 -0.5000 0.0000 0.0000 -0.2500 2y1 66</span></div><div><span style="font-size: 13px;"><br></span></div><div><span style="font-size: 13px;"><br></span></div><div><span style="font-size: 13px;"> The origin shift gives the point of application of the symmetry</span></div><div><span style="font-size: 13px;"> Subtract this vector from all atomic coordinates</span></div><div><span style="font-size: 13px;"> to have this symmetry centered at the origin</span></div><div><span style="font-size: 13px;"><br></span></div><div><span style="font-size: 13px;"><br></span></div><div><span style="font-size: 13px;"> Space group number 19</span></div><div><span style="font-size: 13px;"><br></span></div><div><span style="font-size: 13px;"> Space group P2_12_12_1 (group number 19).</span></div><div><span style="font-size: 13px;"><br></span></div><div><span style="font-size: 13px;"> The Laue class is D_2h (mmm) </span></div><div><span style="font-size: 13px;"><br></span></div><div><span style="font-size: 13px;"> In this class the elastic tensor is</span></div><div><span style="font-size: 13px;"><br></span></div><div><span style="font-size: 13px;"> ( c11 c12 c13 . . . )</span></div><div><span style="font-size: 13px;"> ( c12 c22 c23 . . . )</span></div><div><span style="font-size: 13px;"> ( c13 c23 c33 . . . )</span></div><div><span style="font-size: 13px;"> ( . . . c44 . . )</span></div><div><span style="font-size: 13px;"> ( . . . . c55 . )</span></div><div><span style="font-size: 13px;"> ( . . . . . c66 )</span></div><div><span style="font-size: 13px;"><br></span></div><div><span style="font-size: 13px;"> It requires all six strains.</span></div><div><span style="font-size: 13px;"> for a total of 24 scf calculations</span></div><div><br></div></div><br></div><div><br></div><div dir="ltr" data-setdir="false">In the input file, atomic coordinates were used, the relaxation of which was carried out without considering symmetry (ibrav=0). <span><span style="color: rgb(34, 34, 34); font-family: Arial, Helvetica, sans-serif;">JTH-LDA data sets </span></span>were used (ecutwfc = 81 Ry, occupations = 'tetrahedra_opt', conv_thr = 1.D-8).<br></div></div></font></div><div style=""><font size="3"><br></font></div><div style=""><font size="3">I would be grateful for any ideas to improve the calculation results.</font></div><div style=""><font size="3"><br></font></div><div style="" dir="ltr" data-setdir="false"><font size="3">Thanks,</font></div><div style="" dir="ltr" data-setdir="false"><font size="3">Oleksandr</font></div></div></div></div></body></html>