DiffusionAnalyzer will fail if there is no framework ions

[zhuyizhou]

pymatgen-analysis-diffusion/pymatgen/analysis/diffusion/analyzer.py

Lines 229 to 243 in 5923fb5

	framework_indices = []
	for i, site in enumerate(structure):
	if site.specie.symbol == specie:
	indices.append(i)
	else:
	framework_indices.append(i)
	if self.disp.shape[1] < 2:
	self.diffusivity = 0.0
	self.conductivity = 0.0
	self.diffusivity_components = np.array([0.0, 0.0, 0.0])
	self.conductivity_components = np.array([0.0, 0.0, 0.0])
	self.max_framework_displacement = 0
	else:
	framework_disp = self.disp[framework_indices]
	drift = np.average(framework_disp, axis=0)[None, :, :]

DiffusionAnalyzer will fail if there is no framework ions (namely if all ions are mobile)

Basically if framework_indices is an empty list. The first dimension of framework_disp would be 0. Then drift would be a matrix filled with NAN, which leads to failure in the downstream.

This should a minor bug that is easy to fix.

[shyuep]

Can you put in a fix with a unittest and submit a PR? I think it is relatively simple to test if framework_indices: and then set the drift and displacement.