Cell list Distance module does not support triclinic domains

[RaulPPelaez]

Current implementation of the cell list will fail if the provided box vectors do not represent a rectangular domain:

torchmd-net/torchmdnet/neighbors/neighbors_cuda_cell.cuh

Lines 351 to 354 in e20876f

	TORCH_CHECK(box_size[0][1].item<double>() == 0 && box_size[0][2].item<double>() == 0 &&
	box_size[1][0].item<double>() == 0 && box_size[1][2].item<double>() == 0 &&
	box_size[2][0].item<double>() == 0 && box_size[2][1].item<double>() == 0,
	"Expected \"box_size\" to be diagonal");

Supporting triclinic requires modifying the cell traversal code:

torchmd-net/torchmdnet/neighbors/neighbors_cuda_cell.cuh

Lines 331 to 332 in e20876f

	// Loop over the 27 cells around the current cell
	for (int i = 0; i < 27; i++) {

similarly as how it is done here:
https://github.com/openmm/openmm/blob/master/platforms/reference/src/SimTKReference/ReferenceNeighborList.cpp#L154-L183
This would probably make the current traversal much slower, so maybe it is a good idea to have different kernels for rectangular and triclinic.

[guillemsimeon]

Is this solved?

[RaulPPelaez]

No, but I have it in my list.

[guillemsimeon]

Should I close this, @RaulPPelaez ?

[RaulPPelaez]

No, leave it open. Have not got around it yet.