<html><head></head><body><div class="yahoo-style-wrap" style="font-family:Helvetica Neue, Helvetica, Arial, sans-serif;font-size:16px;"><div dir="ltr" data-setdir="false">Dear QE users & devs!</div><div dir="ltr" data-setdir="false"><br></div><div dir="ltr" data-setdir="false"><div><div>We get the same error using different pseudopotentials (SSSP, LDA, PBEsol) at the final steps of the structure relaxation. I mean the message:</div><div dir="ltr" data-setdir="false"><div><div> </div><div> <i> bfgs failed after 4 scf cycles and 3 bfgs steps, convergence not achieved</i></div><div><i> (criteria: energy < 1.0E-08 Ry, force < 1.0E-08 Ry/Bohr, cell < 1.0E-01 kbar)</i></div><div><i><br></i></div><div><i> End of BFGS Geometry Optimization</i></div><div><br></div></div><br></div><div dir="ltr" data-setdir="false">Using the last geometry (lattice parameters and atomic coordinates) in the next input file, QE takes 4 steps again and stops with the same problem.<br></div><div><br></div><div>We would like to achieve "ideal relaxation" for use in elastic and phonon calculations. Highlights of the input file:</div><div><br></div><div dir="ltr" data-setdir="false"><div><i>&control</i></div><div><i> ....</i></div><div><i> calculation = 'vc-relax',<br></i></div><div><i> forc_conv_thr = 1.0D-8,</i></div><div><i> etot_conv_thr = 1.0D-8,</i></div><div><i> /</i></div><div><i>&SYSTEM</i></div><div><i> celldm(1) = 15.89938814</i></div><div><i> celldm(2) = 1.30410009</i></div><div><i> celldm(3) = 1.47077836</i></div><div><i> ibrav = 8,</i></div><div><i> nat = 104,</i></div><div><i> ntyp = 4,</i></div><div><i> ecutrho = 800</i></div><div><i> ecutwfc = 100</i></div><div><i>/</i></div><div><i>&ELECTRONS</i></div><div><i> conv_thr = 1.D-10, (or 1.D-11)</i></div><div><i> mixing_beta=0.5</i></div><div><i>/</i></div><div><i><br></i></div><div><i>&IONS</i></div><div><i> ion_dynamics = "bfgs"</i></div><div><i>/</i></div><div><i>&CELL</i></div><div><i> cell_dofree = "ibrav"</i></div><div><i> cell_dynamics = "bfgs"</i></div><div><i> press = 0.0</i></div><div><i> press_conv_thr = 0.1</i></div><div dir="ltr" data-setdir="false"><div><div><i><br></i></div><div><i>K_POINTS AUTOMATIC</i></div><div><i>6 5 4 0 0 0</i></div><div><i>(8 6 6 0 0 0)</i></div></div><br></div><div>Restarting the 'vc-relax' calculation several times, we got the following "total force" results:<br></div></div><div dir="ltr" data-setdir="false"><div><div> </div><div>Total force = 0.000080 Total SCF correction = 0.000018</div><div>SCF correction compared to forces is large: reduce conv_thr to get better values</div><div>----------------------------------------------------------------------------------------------</div></div><div dir="ltr" data-setdir="false"><div><div>Total force = 0.000084 Total SCF correction = 0.000037</div><div>SCF correction compared to forces is large: reduce conv_thr to get better values</div><div>----------------------------------------------------------------------------------------------</div></div><div dir="ltr" data-setdir="false"><div><div>Total force = 0.000072 Total SCF correction = 0.000002</div><div>----------------------------------------------------------------------------------------------</div></div><div dir="ltr" data-setdir="false"><div><div>Total force = 0.000072 Total SCF correction = 0.000003</div><div dir="ltr" data-setdir="false"><div><div> Computing stress (Cartesian axis) and pressure</div><div><br></div><div> total stress (Ry/bohr**3) (kbar) P= 0.00</div><div> 0.00000000 0.00000000 0.00000000 0.00 0.00 0.00</div><div> 0.00000000 0.00000001 0.00000000 0.00 0.00 0.00</div><div> 0.00000000 0.00000000 0.00000002 0.00 0.00 0.00</div><div><br></div><div> Message from routine bfgs:</div><div> history already reset at previous step: exiting</div><div> Energy error = 2.4E-09 Ry</div><div> Gradient error = 1.3E-05 Ry/Bohr</div><div> Cell gradient error = 3.1E-03 kbar</div><div>ibrav = 8</div><div> celldm(1) = 15.89938798</div><div> celldm(2) = 1.30409950</div><div> celldm(3) = 1.47077720</div><div>Input lattice vectors:</div><div> 0.99999903 0.00000000 0.00000000</div><div> 0.00000000 1.30409824 0.00000000</div><div> 0.00000000 0.00000000 1.47077577</div><div>New lattice vectors in INITIAL alat:</div><div> 0.99999903 0.00000000 0.00000000</div><div> 0.00000000 1.30409824 0.00000000</div><div> 0.00000000 0.00000000 1.47077577</div><div>New lattice vectors in NEW alat (for information only):</div><div> 1.00000000 0.00000000 0.00000000</div><div> 0.00000000 1.30409950 0.00000000</div><div> 0.00000000 0.00000000 1.47077720</div><div>Discrepancy in bohr = 0.000000 0.000000 0.000000</div><div><br></div><div> bfgs failed after 4 scf cycles and 3 bfgs steps, convergence not achieved</div><div> (criteria: energy < 1.0E-08 Ry, force < 1.0E-08 Ry/Bohr, cell < 1.0E-01 kbar)</div><div><br></div><div> End of BFGS Geometry Optimization</div><div><b>=======================================================</b></div></div><br></div></div><b>next file:</b></div><div dir="ltr" data-setdir="false"><b><br></b></div><div dir="ltr" data-setdir="false"><div><div>Total force = 0.000071 Total SCF correction = 0.000008</div><div>SCF correction compared to forces is large: reduce conv_thr to get better values</div><div>-------------------------------------------------------------------------------------------------</div></div><div><div>Total force = 0.000077 Total SCF correction = 0.000009</div><div>SCF correction compared to forces is large: reduce conv_thr to get better values</div><div>-------------------------------------------------------------------------------------------------</div></div><div dir="ltr" data-setdir="false"><div><div>Total force = 0.000078 Total SCF correction = 0.000000</div><div>--------------------------------------------------------------------------------------------------</div></div><div dir="ltr" data-setdir="false"><div><div>Total force = 0.000082 Total SCF correction = 0.000001</div><div><br></div><div><br></div><div> Computing stress (Cartesian axis) and pressure</div><div><br></div><div> total stress (Ry/bohr**3) (kbar) P= -0.00</div><div> -0.00000001 0.00000000 0.00000000 -0.00 0.00 0.00</div><div> 0.00000000 -0.00000002 0.00000000 0.00 -0.00 0.00</div><div> 0.00000000 0.00000000 -0.00000001 0.00 0.00 -0.00</div><div><br></div><div> Message from routine bfgs:</div><div> history already reset at previous step: exiting</div><div> Energy error = 1.5E-09 Ry</div><div> Gradient error = 2.2E-05 Ry/Bohr</div><div> Cell gradient error = 2.7E-03 kbar</div><div>ibrav = 8</div><div> celldm(1) = 15.89938814</div><div> celldm(2) = 1.30410009</div><div> celldm(3) = 1.47077836</div><div>Input lattice vectors:</div><div> 1.00000001 0.00000000 0.00000000</div><div> 0.00000000 1.30410010 0.00000000</div><div> 0.00000000 0.00000000 1.47077837</div><div>New lattice vectors in INITIAL alat:</div><div> 1.00000001 0.00000000 0.00000000</div><div> 0.00000000 1.30410010 0.00000000</div><div> 0.00000000 0.00000000 1.47077837</div><div>New lattice vectors in NEW alat (for information only):</div><div> 1.00000000 0.00000000 0.00000000</div><div> 0.00000000 1.30410009 0.00000000</div><div> 0.00000000 0.00000000 1.47077836</div><div>Discrepancy in bohr = 0.000000 0.000000 0.000000</div><div><br></div><div> bfgs failed after 4 scf cycles and 3 bfgs steps, convergence not achieved</div><div> (criteria: energy < 1.0E-08 Ry, force < 1.0E-08 Ry/Bohr, cell < 1.0E-01 kbar)</div><div><br></div><div> End of BFGS Geometry Optimization</div><div><b>==========================================================</b></div></div><br></div></div></div></div></div></div><div><br></div><div>We seem to have reached a threshold as the last calculation shows an increase in "total force" and stops with the same problem after 4 steps:</div><div><br></div><div dir="ltr" data-setdir="false"><span> Total force = 0.000082 Total SCF correction = 0.000008</span><br></div><div dir="ltr" data-setdir="false"><span>------------------------------------------------------------------------------------</span></div><div dir="ltr" data-setdir="false"><div><div>Total force = 0.000088 Total SCF correction = 0.000009</div><div>SCF correction compared to forces is large: reduce conv_thr to get better values</div><div>---------------------------------------------------------------------------------------</div></div><div dir="ltr" data-setdir="false"><div><div>Total force = 0.000093 Total SCF correction = 0.000000</div><div>---------------------------------------------------------------------------------------<br></div></div></div><div dir="ltr" data-setdir="false"><div><div>Total force = 0.000105 Total SCF correction = 0.000001</div><div><br></div></div><b>==================================================</b></div></div><div><br></div><div>Questions:</div><div dir="ltr" data-setdir="false">1) What is the acceptable threshold for further calculations of elastic properties? (for example, with the relaxed "Total force = <span>0.000081"</span> we had error of 200% in elastic constants using thermo_pw for tetraborate crystals)</div><div>2) Can the relaxation error be avoided to obtain a more accurate geometry?</div></div><div><br></div><div dir="ltr" data-setdir="false">Thanks in advance!</div><div dir="ltr" data-setdir="false">Oleksandr</div><br></div></div></body></html>