next up previous contents
Next: 5.2 Relax the system Up: 5 Using CP Previous: 5 Using CP Contents

Subsections

5.1 Reaching the electronic ground state

The first step in a CP scheme is to reach the electronic ground state (GS), for a given set of nuclear positions. 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'.

5.1.0.1 Important

Unless you are already experienced with the system you are studying or with the internals of the code, you wil 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 . You could check the value of the fictitious kinetic energy on the standard output (column EKINC).

Different strategies are available to minimize electrons, but the most used ones are:

See the input description to compute the optimal damping factor.


next up previous contents
Next: 5.2 Relax the system Up: 5 Using CP Previous: 5 Using CP Contents
Paolo Giannozzi 2009-10-01