Simple one-center model for linear molecules: application to carbon dioxide.

With computational efficacy in mind, a one-center model for linear molecules is heuristically sketched. When parametrized for CO(2), all parameters save for two are supplied from literature quantum chemistry calculation or, in one case, heuristic argument. Using the remaining two adjustable parameters, the mean unsigned relative errors (predicted/observed) over the temperature range 220-290 K are 4.7% for the energy of vaporization, 0.6% for the liquid, and 8.0% for the vapor coexistence densities, respectively. The critical temperature is estimated at T(c) = 308 K, the critical density at ρ(c) = 0.460 g/cm(3), and the critical pressure at p(c) = 8.26 ± 0.11 MPa. This order of accuracy is comparable to that of many all-atom potential descriptions of CO(2) but is obtained at roughly nine times the speed. When supplied with the experimental bond length, somewhat worse agreement with experiment is exhibited for the neutron-weighted atomic pair distribution function of the liquid. This disparity is tentatively attributed to an overestimated electrostatic quadrupole-quadrupole interaction relative to the other forces present.