Dear QE users & devs! We get the same error using different pseudopotentials (SSSP, LDA, PBEsol) at the final steps of the structure relaxation. I mean the message: bfgs failed after 4 scf cycles and 3 bfgs steps, convergence not achieved (criteria: energy < 1.0E-08 Ry, force < 1.0E-08 Ry/Bohr, cell < 1.0E-01 kbar) End of BFGS Geometry Optimization
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. We would like to achieve "ideal relaxation" for use in elastic and phonon calculations. Highlights of the input file: &control .... calculation = 'vc-relax', forc_conv_thr = 1.0D-8, etot_conv_thr = 1.0D-8, /&SYSTEM celldm(1) = 15.89938814 celldm(2) = 1.30410009 celldm(3) = 1.47077836 ibrav = 8, nat = 104, ntyp = 4, ecutrho = 800 ecutwfc = 100/&ELECTRONS conv_thr = 1.D-10, (or 1.D-11) mixing_beta=0.5/ &IONS ion_dynamics = "bfgs"/&CELL cell_dofree = "ibrav" cell_dynamics = "bfgs" press = 0.0 press_conv_thr = 0.1 K_POINTS AUTOMATIC6 5 4 0 0 0(8 6 6 0 0 0) Restarting the 'vc-relax' calculation several times, we got the following "total force" results: Total force = 0.000080 Total SCF correction = 0.000018SCF correction compared to forces is large: reduce conv_thr to get better values----------------------------------------------------------------------------------------------Total force = 0.000084 Total SCF correction = 0.000037SCF correction compared to forces is large: reduce conv_thr to get better values----------------------------------------------------------------------------------------------Total force = 0.000072 Total SCF correction = 0.000002----------------------------------------------------------------------------------------------Total force = 0.000072 Total SCF correction = 0.000003 Computing stress (Cartesian axis) and pressure total stress (Ry/bohr**3) (kbar) P= 0.00 0.00000000 0.00000000 0.00000000 0.00 0.00 0.00 0.00000000 0.00000001 0.00000000 0.00 0.00 0.00 0.00000000 0.00000000 0.00000002 0.00 0.00 0.00 Message from routine bfgs: history already reset at previous step: exiting Energy error = 2.4E-09 Ry Gradient error = 1.3E-05 Ry/Bohr Cell gradient error = 3.1E-03 kbaribrav = 8 celldm(1) = 15.89938798 celldm(2) = 1.30409950 celldm(3) = 1.47077720Input lattice vectors: 0.99999903 0.00000000 0.00000000 0.00000000 1.30409824 0.00000000 0.00000000 0.00000000 1.47077577New lattice vectors in INITIAL alat: 0.99999903 0.00000000 0.00000000 0.00000000 1.30409824 0.00000000 0.00000000 0.00000000 1.47077577New lattice vectors in NEW alat (for information only): 1.00000000 0.00000000 0.00000000 0.00000000 1.30409950 0.00000000 0.00000000 0.00000000 1.47077720Discrepancy in bohr = 0.000000 0.000000 0.000000 bfgs failed after 4 scf cycles and 3 bfgs steps, convergence not achieved (criteria: energy < 1.0E-08 Ry, force < 1.0E-08 Ry/Bohr, cell < 1.0E-01 kbar) End of BFGS Geometry Optimization======================================================= next file: Total force = 0.000071 Total SCF correction = 0.000008SCF correction compared to forces is large: reduce conv_thr to get better values-------------------------------------------------------------------------------------------------Total force = 0.000077 Total SCF correction = 0.000009SCF correction compared to forces is large: reduce conv_thr to get better values-------------------------------------------------------------------------------------------------Total force = 0.000078 Total SCF correction = 0.000000--------------------------------------------------------------------------------------------------Total force = 0.000082 Total SCF correction = 0.000001 Computing stress (Cartesian axis) and pressure total stress (Ry/bohr**3) (kbar) P= -0.00 -0.00000001 0.00000000 0.00000000 -0.00 0.00 0.00 0.00000000 -0.00000002 0.00000000 0.00 -0.00 0.00 0.00000000 0.00000000 -0.00000001 0.00 0.00 -0.00 Message from routine bfgs: history already reset at previous step: exiting Energy error = 1.5E-09 Ry Gradient error = 2.2E-05 Ry/Bohr Cell gradient error = 2.7E-03 kbaribrav = 8 celldm(1) = 15.89938814 celldm(2) = 1.30410009 celldm(3) = 1.47077836Input lattice vectors: 1.00000001 0.00000000 0.00000000 0.00000000 1.30410010 0.00000000 0.00000000 0.00000000 1.47077837New lattice vectors in INITIAL alat: 1.00000001 0.00000000 0.00000000 0.00000000 1.30410010 0.00000000 0.00000000 0.00000000 1.47077837New lattice vectors in NEW alat (for information only): 1.00000000 0.00000000 0.00000000 0.00000000 1.30410009 0.00000000 0.00000000 0.00000000 1.47077836Discrepancy in bohr = 0.000000 0.000000 0.000000 bfgs failed after 4 scf cycles and 3 bfgs steps, convergence not achieved (criteria: energy < 1.0E-08 Ry, force < 1.0E-08 Ry/Bohr, cell < 1.0E-01 kbar) End of BFGS Geometry Optimization========================================================== 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: Total force = 0.000082 Total SCF correction = 0.000008 ------------------------------------------------------------------------------------Total force = 0.000088 Total SCF correction = 0.000009SCF correction compared to forces is large: reduce conv_thr to get better values---------------------------------------------------------------------------------------Total force = 0.000093 Total SCF correction = 0.000000--------------------------------------------------------------------------------------- Total force = 0.000105 Total SCF correction = 0.000001 ================================================== Questions:1) What is the acceptable threshold for further calculations of elastic properties? (for example, with the relaxed "Total force = 0.000081" we had error of 200% in elastic constants using thermo_pw for tetraborate crystals)2) Can the relaxation error be avoided to obtain a more accurate geometry? Thanks in advance!Oleksandr
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