CALCULATION OF THE FREE-ENERGY OF SOLVATION OF THE LI+ AND NA+ IONS IN WATER AND CHLOROFORM

The free energies of solvation of the lithium and sodium cations in wa ter and in chloroform were calculated using Monte Carlo computer simul ations. The free energies were obtained using thermodynamic integratio n either on a nearly linear path or on a polynomial path and the integ ral was evaluated with a Gaussian quadrature. The precision of the res ults was confirmed through comparison with additional calculations tha t obtained the solvation free energy differences by mutating a lithium to a sodium cation. Three sources for the discrepancy between the cal culated and experimental solvation free energies were considered: the multibody terms were estimated using a polarization model; the long-ra nge contributions were estimated with the Born correction and with a c alculation using larger system size; and the extent of charge transfer was examined by ab initio calculations based on complete solvation sh ells extracted from the simulation.