  Graphynes are novel two-dimensional carbon-based materials that -due to their
nanoweb-like structure- have been proposed as molecular filters, especially for
water purification technologies. In this work 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. Nevertheless, for
graphdiyne, which presents a pore size almost matching that of water, a low
barrier is found which in turn disappears if an active hydrogen bond with an
additional water molecule on the opposite side of the opening is taken into
account. These results support the possibility of using graphtriyne as an
efficient membrane for water filtration but, in contrast with previous
determinations, they do not exclude graphdiyne. In fact, the related first
principles penetration barrier leads to water permeation probabilities which
are at least two order of magnitude larger than those estimated by employing
commonly used force fields. A new pair potential for the water--carbon
non-covalent component of the interaction has been built and it is recommended
for molecular dynamics simulation involving graphdiyne and water.
