Keywords: user_guide

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## 4.1 Reaching the electronic ground state

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. 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:

- steepest descent: `electron_dynamics = 'sd'`
- damped dynamics: `electron_dynamics = 'damp'`, `electron_damping` = a number typically ranging from 0.1 and 0.5

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