Ab initio quantum mechanical simulations confirm the formation of all postulated species in ionic dissociation

Abstract

A single sodium chloride molecule in aqueous solution was simulated by the ab initio quantum mechanical charge field-molecular dynamics (QMCF-MD) approach. During a series of simulations the solvated molecule (CIP), dissociated solvated ions and -most noticeably -a solvent separated ion pair (SSIP) were observed and the structural and dynamical characteristics of these systems were investigated. In addition to a detailed structural analysis of the observed species, vibrational spectra and charge distributions were calculated to elucidate the mechanism of the NaCl dissociation.

Three‐body expansion of the fragment molecular orbital method combined with density‐functional tight‐binding

“…In this work, the accuracy of FMO‐DFTB/MD has been evaluated for solvated sodium cation, and 100 ps MD simulations have been performed to obtain the radial distribution and coordination number of sodium cation in solution. The obtained coordination number of sodium (6.5) is in reasonable agreement with other studies (5–6) . Adding periodic boundary conditions (PBC) to FMO/MD in future will be useful; at present, the use of PBC in QM/MD is not available in production GAMESS‐US, although some development of PBC for FMO has been reported …”

“…The obtained coordination number of sodium (6.5) is in reasonable agreement with other studies (5)(6). [88][89][90][91] Adding periodic boundary conditions (PBC) to FMO/MD in future will be useful; at present, the use of PBC in QM/MD is not available in production GAMESS-US, although some development of PBC for FMO has been reported. [98,99]…”

“…There are many studies on the CN of O around Na ; it is suggested on the basis of simulations that it is between 5 and 6 . The values in DFTB and FMO3‐DFTB are slightly overestimated, and the FMO2‐DFTB value is much overestimated.…”

“…There are many studies on the CN of O around Na 1 ; it is suggested on the basis of simulations that it is between 5 and 6. [88][89][90][91] The values in DFTB and FMO3-DFTB are slightly overestimated, and the FMO2-DFTB value is much overestimated. This is in agreement with the results of relative energies and Mulliken charges discussed above.…”

Physicochemical Properties of Ion Pairs of Biological Macromolecules

“…In principle, this is not the case for ab initio MD. However, ab initio MD is computationally expensive and its applicability to ion pairs is currently limited to small systems and a short timescale (<100 ps) [ 164 , 165 , 166 ]. Improvement in computational speed may enable applications of ab initio MD to biological ion pairs over a longer timescale.…”