[Pw_forum] Total forces not converging: relax calculation

[Daniel Reta]

Dear all,

I am running a calculation to optimize the atomic position within the cell. I am using a large ecutwfc value (110 Ry) because I am using nor-conserving pp. I will have to later check this value against the phonons, since it is this property the one I want to study. When I grep the Total force values I get this

     Total force =     2.649777     Total SCF correction =     0.000385
     Total force =     1.693758     Total SCF correction =     0.000589
     Total force =     0.484600     Total SCF correction =     0.000552
     Total force =     0.280971     Total SCF correction =     0.000235
     Total force =     0.118901     Total SCF correction =     0.000730
     Total force =     0.105601     Total SCF correction =     0.000207
     Total force =     0.087956     Total SCF correction =     0.000233
     Total force =     0.067168     Total SCF correction =     0.000242
     Total force =     0.051189     Total SCF correction =     0.000217
     Total force =     0.040092     Total SCF correction =     0.000241
     Total force =     0.033889     Total SCF correction =     0.000143
     Total force =     0.030175     Total SCF correction =     0.000155
     Total force =     0.026895     Total SCF correction =     0.000098
     Total force =     0.025422     Total SCF correction =     0.000163
     Total force =     0.024484     Total SCF correction =     0.000153
     Total force =     0.023613     Total SCF correction =     0.000056
     Total force =     0.020151     Total SCF correction =     0.000127
     Total force =     0.017819     Total SCF correction =     0.000108
     Total force =     0.018180     Total SCF correction =     0.000056
     Total force =     0.017125     Total SCF correction =     0.000056
     Total force =     0.015261     Total SCF correction =     0.000150
     Total force =     0.014572     Total SCF correction =     0.000125
     Total force =     0.015588     Total SCF correction =     0.000104
     Total force =     0.015453     Total SCF correction =     0.000067
     Total force =     0.012640     Total SCF correction =     0.000044
     Total force =     0.011777     Total SCF correction =     0.000120
     Total force =     0.011944     Total SCF correction =     0.000098
     Total force =     0.011262     Total SCF correction =     0.000052
     Total force =     0.010667     Total SCF correction =     0.000069
     Total force =     0.011162     Total SCF correction =     0.000061
     Total force =     0.012045     Total SCF correction =     0.000091

It seems it got stuck and is unable to descent further, despite the SCF correction is almost zero. 

I am using the standard values for the &IONS specifications

 &IONS
    ion_dynamics='bfgs'
    ion_positions='default'
 /

with 

 &electrons
    conv_thr=1.D-7
 /

Could you please refer me to keywords or strategies that are sensible to the force convergence?

Best regards

========================

Dr. Daniel Reta,
Post-doctoral Research Associate,
Computational Chemistry, School of Chemistry
University of Manchester

Email: daniel.reta at manchester.ac.uk

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