[Kwant] Convergence of default solver near resonances

[dreitz]

Hello all,

In follow-up to a recent question "Numerical precision of smatrix" 
https://mail.python.org/archives/list/kwant-discuss@python.org/thread/LZ22XLVMJIVBSGHX5WXYHE4B4GOZQGCH/
 , I am also having issues with numerical precision and/or convergence of the 
wave functions inside the scattering region when using the default solver. 
Specifically, I am calculating tunnel couplings from a lead to a well through a 
barrier. There are resonances in the density of states at the energies of bound 
states inside the well, whose linewidth depends on the barrier height. When the 
resonances become too sharp, the DOS computed by Kwant becomes choppy and loses 
its well defined resonance characteristics. How can I improve the 
tolerance/precision of this calculation?

The code to compute the DOS would look like this:
        wfs = kwant.wave_function(sys,energy=energy);
        wf = wfs(leadNum)[leadBandNum]
        rho = kwant.operator.Density(sys);
        density = rho(wf);

Thanks,
Derek