title: A new force field of formamide and the effect of the dielectric constant on miscibility.
abstract: Current force fields underestimate significantly the dielectric constant of formamide at standard conditions. We present a derivation of an accurate potential for formamide, with a functional form based on the OPLS/AA force field. Our procedure follows the approach introduced by Salas et al. ( J. Chem. Theory Comput. 2015 , 11 , 683 - 693 ) that relies on ab initio calculations and molecular dynamics simulations. We consider several strategies to derive the atomic charges of formamide. We find that the inclusion of polarization effects in the quantum mechanical computations is essential to obtain reliable force fields. By varying the atomic charges and the Lennard-Jones parameters describing the dispersion interactions in the OPLS/AA force field, we derive an optimum set of parameters that provides accurate results for the dielectric constant, surface tension, and bulk density of liquid formamide in a wide range of thermodynamic states. We test the transferability of our parameters to investigate liquid/liquid mixtures. We have chosen as case study an equimolar mixture of formamide and hexan-2-one. This mixture involves two fluids with very different polar characteristics, namely, large differences in their dielectric constants and their performance as solvents. The new potential predicts a liquid/liquid phase separation, in good agreement with experimental data, and highlights the importance of the correct parametrization of the pure liquid phases to investigate liquid mixtures. Finally, we examine the microscopic origin of the observed inmiscibility between formamide and hexa-2-one.
authors.affiliation: Departamento de Química, Universidad Autónoma Metropolitana-Iztapalapa , Avenida San Rafael Atlixco 186, Col. Vicentina, 09340 México Distrito Federal, México.
authors.forename: Alexander Pérez
authors.initials: AP
authors.lastname: de la Luz
authors.affiliation: Departamento de Química, Universidad Autónoma Metropolitana-Iztapalapa , Avenida San Rafael Atlixco 186, Col. Vicentina, 09340 México Distrito Federal, México.
authors.forename: G Arlette
authors.initials: GA
authors.lastname: Méndez-Maldonado
authors.affiliation: Departamento de Química, Universidad Autónoma Metropolitana-Iztapalapa , Avenida San Rafael Atlixco 186, Col. Vicentina, 09340 México Distrito Federal, México.
authors.forename: Edgar
authors.initials: E
authors.lastname: Núñez-Rojas
authors.affiliation: Department of Chemistry, Imperial College London , London SW7 2AZ, United Kingdom.|Department of Chemistry, Norwegian University of Science and Technology , NO-7491 Trondheim, Norway.
authors.forename: Fernando
authors.initials: F
authors.lastname: Bresme
authors.affiliation: Departamento de Química, Universidad Autónoma Metropolitana-Iztapalapa , Avenida San Rafael Atlixco 186, Col. Vicentina, 09340 México Distrito Federal, México.
authors.forename: José
authors.initials: J
authors.lastname: Alejandre