Computation of methodology-independent single-ion solvation properties from molecular simulations. III. Correction terms for the solvation free energies, enthalpies, entropies, heat capacities, volumes, compressibilities, and expansivities of solvated ions

• Published in: The Journal of chemical physics 2011-04, Vol.134 (14), p.144103-144103-30
• Main Authors: Reif, Maria M., Hünenberger, Philippe H.
• Format: Article
• Language: English
• Subjects: Algorithms; Chemistry, Physical - methods; Computer Simulation; Ions - chemistry; Models, Molecular; Solutions - chemistry; Static Electricity; Temperature; Thermodynamics; Water - chemistry
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.3567020

The raw single-ion solvation free energies computed from atomistic (explicit-solvent) simulations are extremely sensitive to the boundary conditions (finite or periodic system, system or box size) and treatment of electrostatic interactions (Coulombic, lattice-sum, or cutoff-based) used during these simulations. However, as shown by Kastenholz and Hünenberger [ J. Chem. Phys. 124 , 224501 ( 2006 )] 10.1529/biophysj.106.083667 , correction terms can be derived for the effects of: (A) an incorrect solvent polarization around the ion and an incomplete or/and inexact interaction of the ion with the polarized solvent due to the use of an approximate (not strictly Coulombic) electrostatic scheme; (B) the finite-size or artificial periodicity of the simulated system; (C) an improper summation scheme to evaluate the potential at the ion site, and the possible presence of a polarized air-liquid interface or of a constraint of vanishing average electrostatic potential in the simulated system; and (D) an inaccurate dielectric permittivity of the employed solvent model. Comparison with standard experimental data also requires the inclusion of appropriate cavity-formation and standard-state correction terms. In the present study, this correction scheme is extended by: (i) providing simple approximate analytical expressions (empirically-fitted) for the correction terms that were evaluated numerically in the above scheme (continuum-electrostatics calculations); (ii) providing correction terms for derivative thermodynamic single-ion solvation properties (and corresponding partial molar variables in solution), namely, the enthalpy, entropy, isobaric heat capacity, volume, isothermal compressibility, and isobaric expansivity (including appropriate standard-state correction terms). The ability of the correction scheme to produce methodology-independent single-ion solvation free energies based on atomistic simulations is tested in the case of Na + hydration, and the nature and magnitude of the correction terms for derivative thermodynamic properties is assessed numerically.