Solutions to common problems

If you run into an issue that isn’t covered below, please file an issue or reach us on Discord — we will do our best to help.

Calculation does not converge

Quite often the self-consistent iterations will not lead to a converged solution. There are several possible causes for calculation to diverge, the two main reasons are:

• Self-consistent iterations are unstable;
• Non-uniform Fourier transform has a large leakage.

Instability of self-consistent iterations

When the initial starting point of the self-consistent iterations lays far away from the solution, iterative solver may experience one of the following behavior: diverge, oscilate between multiple meta-stable points, show no pattern of divergence or convergence.

To stabilize the self-consistent iterations Green provides several options. By default we choose to use a simple mixing of the self-energy, where the self-energy at the current iteration is mixed with the self-energy from the previous iteration. Adjusting the mixing parameter (choosing smaller value for --mixing_weight parameter) can usually stabilize convergence but makes it slower. In many cases the better option is to use advanced convergence acceleration techniques, such as direct inversion in the iterative subspace (DIIS) method. For more details on how to use it read the DIIS tutorial.

Large leakage in non-uniform Fourier transformation

All dynamical quantites in Green use non-uniform compact representation in imaginary time/Matsubara frequency domain. The choice of non-uniform grid has to address two main aspects:

• being compact to reduce computational complexity;
• being large enough to properly capture short time/large frequency asymptotic behavior.

If the grid is too small large spectral leakage can occure during the Foruier transfrom in time/frequency domain, that may result in large calculation errors and potentially break down of self-consistent iterations. During the calculations, Green computes the spectral leakage every time the Fourier transfrom in time/frequency domain is performed. If the spectral leakage is larger than $10^{-8}$ the following warning message will be printed into standard output:

WARNING: The leakage is larger than 1e-8

When the Green/WeakCoupling simulations are done in single precision, spectral leakage will almost always exceed $10^{-8}$ cutoff and we suggest to monitor spectral leakage for couple of iterations and if it does not grow, the calculations are expected to be stable and no further actions are needed.

Build and installation problems

CMake configure fails with “detected dubious ownership”

CMake uses git internally to clone sub-dependencies via FetchContent. On shared filesystems or in containers where the directory owner differs from the current user, git refuses to operate and FetchContent fails with a message such as:

fatal: detected dubious ownership in repository at '/path/to/build/_deps/...'

The fix is to tell git to trust the affected directories:

git config --global --add safe.directory '*'

GPU build fails: nvcc fatal: Unsupported gpu architecture 'compute_70'

CUDA 13 dropped support for sm_70 (Volta) and sm_75 (Turing). If you are on CUDA 13 or later, pass -DGPU_ARCHS to target only your GPU’s architecture instead of relying on the default list:

nvidia-smi --query-gpu=compute_cap --format=csv,noheader

Use the reported value with the dot removed (e.g. 8.9 → 89) in the CMake configure step:

cmake -S green-mbpt -B green-mbpt-build \
    -DCMAKE_BUILD_TYPE=Release            \
    -DCUSTOM_KERNELS="https://github.com/Green-Phys/green-gpu" \
    -DGPU_ARCHS="89"