Mulliken population charges for the water dimer from X-POL. AM1 denotes a full AM1 calculation for the water dimer, SX-POL denotes the self-consistent but not variational X-POL potential. X-POL denotes the variational result obtained using the equations of the present article. Cartesian coordinates (in Å) used for the water dimer are O1(−6.302 51,2.127 23,0.823 74), H11(−6.891 82,2.556 39,1.444 04), H12(−5.736 54,1.587 07,1.375 23), O2(−5.610 42,3.122 60,−1.661 72), H21(−6.136 34,2.539 42,−2.209 02), and H22(−5.804 20,2.830 43,−0.771 04).