The first run, when starting from scratch, is always an electronic minimization, with fixed ions and cell, to bring the electronic system on the ground state (GS) relative to the starting atomic configuration. This step is conceptually very similar to self-consistency in a pw.x run.
Sometimes a single run is not enough to reach the GS. In this case, you need to re-run the electronic minimization stage. Use the input of the first run, changing restart_mode = 'from_scratch' to restart_mode = 'restart'.
NOTA BENE: Unless you are already experienced with the system you are studying or with the internals of the code, you will usually need to tune some input parameters, like emass, dt, and cut-offs. For this purpose, a few trial runs could be useful: you can perform short minimizations (say, 10 steps) changing and adjusting these parameters to fit your needs. You can specify the degree of convergence with these two thresholds:
etot_conv_thr: total energy difference between two consecutive steps
ekin_conv_thr: value of the fictitious kinetic energy of the electrons.
Usually we consider the system on the GS when
ekin_conv_thr < 10-5
Different strategies are available to minimize electrons, but the most used
ones are:
See the input description to compute the optimal damping factor.
Next: 4.2 Relax the system
Up: 4 Using CP
Previous: 4 Using CP
Contents
Layla Martin-Samos Colomer
2012-05-11