1 a.u. corresponds to
2 Ry = 27.21161 eV = 627.5095 kcal/mol = 2625.5 kJ/mol = 219474.63067 /cm ~ 1050 kT ~ 0.529177248 Å ~ 9.1093897 x 10^-31 kg ~ 0.02418884 fs,  

N_A = 6.0221415x10^23 /mol

R = 8.314472(15) J/(K·mol)

pi = 3.14159265358979323846