Density value P calculated from the crystal cell and contents,
expressed as per cent solvent.
P = 1 - (1.23 N MMass) / V
N = the number of molecules in the unit cell
MMass = the molecular mass of each molecule (gm/mole)
V = the volume of the unit cell (A3)
1.23 = a conversion factor evaluated as:
(0.74 cm3/g) (1024 A3/cm3)
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(6.02*1023) molecules/mole
where 0.74 is an assumed value for the partial specific
volume of the molecule