I too have experienced significant innacuracies with the sparse solver depending on system parameters. My work around was to use a dense solver instead, this might be an option for you if your system is too large.
- [Kwant] Numerical precision of smatrix Jannis Neuhaus-Steinmetz
- [Kwant] Re: Numerical precision of smatrix Henry Axt
- [Kwant] Re: Numerical precision of smatrix Anton Akhmerov
