changed SumCalculator method of computing stresses
changed SumCalculator method of computing stresses when 3x3 tensor is passed instead of Voigt notation
The command calculator.get_property('stress', atoms)
can return either the full 3x3 stress tensor or the 6x1 array in Voigt notation. Different calculators default to different behaviors (e.g., the DFTD4 calculator uses Voigt notation and the M3GNetCalculator uses the full 3x3 tensor), which caused bugs in the SumCalculator
in some cases. This change changes all stress calculations in the SumCalculator
to the Voigt notation using the methods from the get_stress()
function in ase/atoms
.