The intramolecular bond lengths of the donor BEDT-TTF (bis(ethylenedit
hio)tetrathiafulvalene, also ET) are sensitive to the charge carried b
y the molecule. By considering a large number of ET salts, we have dev
eloped a method for determining experimentally the charges of the ET m
olecules. The standard deviation in charge is only 0.1 for high qualit
y structures.