The electronic density of all elements in the first three rows of the periodic table are approximated by three s-type Gaussian functions. Their weights are determined by least squares minimization from DFT calculations using the B3LYP functional with the GD3 empirical dispersion correction . The small Effective Core Potential (ECP) and basis-set CEP-31G was used for all atoms except H and He where the all-electron basis-set cc-pVDZ was taken. A Mulliken population analysis compensates for charge redistribution of the isolated fragments (see supplementary material for more details), effectively neglecting any charge redistribution when two molecules are coming in close contact. Due to the ECP basis-set which we use, the charges on the nuclei of the molecules are equal to the number of their valence electrons.