In the units section, real units have grams/mole for mass and angstroms for distance. In that case density should be in grams/angstroms cube.
For granular atom styles, the density for atoms gets very small in that case. How do we enter this small number. Is there any option to enter in scientific format? I tried to enter in g/cm cube just to see if I can run granular style. It gave segmentation fault. I am thinking the big density values I entered may be the reason. I did not try writing 24 decimal digits!