Title: Electrostatic and induction effects in the solubility of water in alkanes,
Abstract: Experiments show that at 298~K and 1 atm pressure the transfer free energy,
$\mu^{\rm ex}$, of water from its vapor to liquid normal alkanes $C_nH_{2n+2}$
($n=5\ldots12$) is negative. Earlier it was found that with the united-atom
TraPPe model for alkanes and the SPC/E model for water, one had to artificially
enhance the attractive alkane-water cross interaction to capture this behavior.
Here we revisit the calculation of $\mu^{\rm ex}$ using the polarizable AMOEBA
and the non-polarizable Charmm General (CGenFF) forcefields. We test both the
AMOEBA03 and AMOEBA14 water models; the former has been validated with the
AMOEBA alkane model while the latter is a revision of AMOEBA03 to better
describe liquid water. We calculate $\mu^{\rm ex}$ using the test particle
method. With CGenFF, $\mu^{\rm ex}$ is positive and the error relative to
experiments is about 1.5 $k_{\rm B}T$. With AMOEBA, $\mu^{\rm ex}$ is negative
and deviations relative to experiments are between 0.25 $k_{\rm B}T$ (AMOEBA14)
and 0.5 $k_{\rm B}T$ (AMOEBA03). Quantum chemical calculations in a continuum
solvent suggest that zero point effects may account for some of the deviation.
Forcefield limitations notwithstanding, electrostatic and induction effects,
commonly ignored in considerations of water-alkane interactions, appear to be
decisive in the solubility of water in alkanes.