Polarizable Molecular Simulations Reveal How Silicon-Containing Functional Groups Govern the Desalination Mechanism in Nanoporous Graphene

We report a molecular dynamics (MD) simulation study of reverse osmosis desalination using nanoporous monolayer graphene passivated by SiH₂ and Si­(OH)₂ functional groups. A highly accurate and detailed polarizable molecular mechanics force field model was developed for simulating graphene nanopores of various sizes and geometries. The simulated water fluxes and ion rejection percentages are explained using detailed atomistic mechanisms derived from analysis of the simulation trajectories. Our main findings are as follows: (1) The Si­(OH)₂ pores possess superior ion rejection rates due to selective electrostatic repulsion of Cl^– ions, but Na⁺ ions are attracted to the pore and block water transfer. (2) By contrast, the SiH₂ pores operate via a steric mechanism that excludes ions based on the size and flexibility of their hydration layers. (3) In the absence of ions, water flux is directly proportional to the solvent accessible area within the pore; however, simulated fluxes are lower than those inferred from recent experimental work. We also provide some hypotheses that could resolve the differences between simulation and experiment

BeCH₂: The Simplest Metal Carbene. High Levels of Theory

The simplest metal carbene, BeCH₂, is experimentally unknown. Its isomer, HBeCH, lies higher in energy, but has been detected by the infrared matrix isolation [<i>J. Am. Chem. Soc.</i> <b>1998</b>, <i>120</i>, 6097]. In the present study the ground and low-lying excited states of the BeCH₂ and HBeCH isomers were investigated using state-of-the-art ab initio methods, including coupled-cluster theory with up to full quadruple excitations (CCSDTQ), and complete active space self-consistent field (CASSCF) with multireference configuration interaction with single and double excitations (MRCISD). The relative energies were obtained using the focal point analysis combined with large correlation-consistent cc-pCVXZ basis sets (X = D, T, Q, 5) and were extrapolated to the complete basis set (CBS) limit. The ³B₁ state of BeCH₂ (<i>C</i>_2<i>v</i> symmetry) is the global minimum on the ground triplet potential energy surface (PES). The ³Σ^– state of the linear isomer HBeCH is located 4.9 kcal mol^–1 above the global minimum, at the CCSDTQ/CBS level of theory. The BeCH₂ and HBeCH isomers are connected through the ³A″ transition state lying 46.1 kcal mol^–1 above the global minimum. The higher-lying energy HBeCH structure has much larger Be–C bond dissociation energy (126.6 kcal mol^–1, cf. BDE­(BeCH₂) = 62.1 kcal mol^–1). The lowest excited state of BeCH₂ is the open-shell ¹B₁ state, with a relative energy of only 4.9 kcal mol^–1 above the global minimum, followed by ¹A₁ state (16.8 kcal mol^–1) at the MRCISD/cc-pCVQZ level of theory. For the HBeCH isomer the lowest-energy excited states are ¹Δ and ¹Σ⁺, lying about 30 kcal mol^–1 above the global minimum. For the ground state of BeCH₂ the fundamental vibrational frequencies computed using second-order vibrational perturbation theory (VPT2) at the CCSD­(T)/cc-pCVQZ level are reported. We hope that our highly accurate theoretical results will assist in the experimental identification of BeCH₂

Additional file 1 of The Effect of immunonutrition in patients undergoing pancreaticoduodenectomy: a systematic review and meta-analysis

Supplementary Material