Chemical potentials control

Ajusting of chemical potentials

Static codes adjust chemical potentials automatically in such a way as to provide a solution with the requested particle number. The following parameters control the adjusting process:

muchange                0.5      # coefficient for changing chemical potential, default=0.5, for both components
# muchange_a              0.5      # or you can control muchange for each component separately using tags with `a` ...
# muchange_b              0.5      # ... and `b` suffixes. 
mumaxchange             0.05     # maximal amount that chemical potential can change between iterations, in units of Fermi energy
# mumaxchange_a           0.05     # or you can control mumaxchange for each component separately using tags with `a` ...
# mumaxchange_b           0.05     # ... and `b` suffixes. 

Chemical potentials are adjusted according to the rule:

$$\begin{aligned} \Delta\mu_{\sigma}^{(i)} &= \textrm{muchange}_{\sigma}\,\frac{N_{\sigma}^{(\textrm{req.})}-N_{\sigma}^{(i)}}{N_{\sigma}^{(\textrm{req.})}}\\\ \textrm{if}\,|\Delta\mu_{\sigma}^{(i)}/\varepsilon_F|&>\textrm{mumaxchange}_{\sigma}:\,\textrm{decrease}\,\textrm{magnitude}\,\textrm{of}\,\Delta\mu_{\sigma}^{(i)}\\\ \mu_{\sigma}^{(i+1)} &= \mu_{\sigma}^{(i)} + \Delta\mu_{\sigma}^{(i)} \end{aligned}$$

Fixed chemical potential mode

To execute calculations for fixed chemical potential, you need to set in input file:

muchange                0.0      # do not change chemical potential
npartconveps            1.0e+9   # ignore checking of particle number convergence criteria

In addition, you need to set the value of chemical potentials. For this use process_params function in problem-definition.h

void process_params(double *params, double *kF, double *mu, size_t extra_data_size, void *extra_data)
{
   // hard set of chemical potentials
   mu[SPINA] = YOUR_VALUE; // <-- you can promote it as user-defined parameter
   mu[SPINB] = YOUR_VALUE; // <-- you can promote it as user-defined parameter

   // ...
}