Penetration Barrier of Water through Graphynes’ Pores: First-Principles Predictions and Force Field Optimization

Graphynes are novel two-dimensional carbon-based materials that have been proposed as molecular filters, especially for water purification technologies. We carry out first-principles electronic structure calculations at the MP2C level of theory to assess the interaction between water and graphyne, graphdiyne, and graphtriyne pores. The computed penetration barriers suggest that water transport is unfeasible through graphyne while being unimpeded for graphtriyne. For graphdiyne, with a pore size almost matching that of water, a low barrier is found that in turn disappears if an active hydrogen bond with an additional water molecule on the opposite side of the opening is considered. Thus, in contrast with previous determinations, our results do not exclude graphdiyne as a promising membrane for water filtration. In fact, present calculations lead to water permeation probabilities that are 2 orders of magnitude larger than estimations based on common force fields. A new pair potential for the water–carbon noncovalent component of the interaction is proposed for molecular dynamics simulations involving graphdiyne and water

Global potentials for the interaction between rare gases and graphene-based surfaces: An atom-bond pairwise additive representation

Global potentials for the physisorption of rare-gas atoms on graphene and graphite, amenable for a variety of dynamics simulations, are reported. An atom-bond pairwise additive form of the potential is used, where the interaction pairs, represented by proper analytical functions, are constituted by the Rg atom (Rg = He, Ne, Ar, Kr) and the C-C bonds of the graphene sheet(s). The parameters of the atom-bond pair potential, derived from the polarizability of the interacting partners, are fine-tuned, exploiting calculations of the prototypical Rg-coronene system using high-level electronic structure methods and large basis sets. The atom-graphene/graphite potential is further expanded in a Fourier series, and it is found that for an accurate representation of the interaction only a small number of corrugation terms need to be added to the laterally averaged potential. Furthermore, this corrugation part of the potential is both identical for Rg-graphene and Rg-graphite; in other words, inner layers of graphite only play a role in the laterally averaged Rg-graphite potential. For all systems, the hollow at the center of the carbon ring is the preferred adsorption site, although diffusion barriers are low. The present results compare well with previous data regarding well depths and equilibrium distances at different adsorption sites and, for graphite, the long-range dispersion coefficient C3. In addition, binding energies (eigenvalues of the laterally averaged potentials) are in a fairly good agreement with experimental determinations, providing further support for the reliability of the potentials. © 2013 American Chemical Society.The work has been funded by Spanish grants FIS2010-22064- C02-02 and CSD2009-00038. Allocation of computing time by CESGA (Spain) and the COST-CMTS Action CM1002 “Convergent Distributed Environment for Computational Spectroscopy (CODECS)” are also acknowledged. F.P. acknowledges financial support from the Italian Ministry of University and Research (MIUR) for PRIN contracts.Peer Reviewe

Analytical Gradients of Hartree-Fock Exchange with Density Fitting Approximations

We extend the local exchange (LK) algorithm [Aquilante, F.; Pedersen, T. B.; Lindh, R. J. Chem. Phys. 2007, 126, 194106] to the calculation of analytical gradients with density fitting. We discuss the features of the screening procedure and demonstrate the possible advantages of using this formulation, which is easily interfaced to a standard integral-direct gradient code. With auxiliary basis sets obtained from Cholesky decomposition of atomic or molecular integral blocks with a decomposition threshold of 10(-4)E(h), typical errors due to the density fitting in bond lengths, bond angles, and dihedral angles are 0.1 pm, 0.1 degrees, and 0.5 degrees, respectively. The overall speedup of geometry optimizations is about 1 order of magnitude for atomic natural-orbital-type basis sets but much less pronounced for correlation-consistent basis sets