Molecular Simulations of Structure, Dynamics and Spectral Properties of Aqueous Solutions using Polarizable Forcefields
Deepikaa) and Amalendu Chandrab)
Department of Chemistry, Indian Institute of Technology Kanpur, India 208016
THz spectroscopy is an important tool which can detect solute induced changes of the collective water network dynamics [1]. Far infrared or terahertz (THz) spectroscopy offers another useful method for probing the structure and dynamics of salt solutions and specific ion effects. The usefulness of THz spectroscopy lies partially in the fact that it involves a frequency range that is low enough that ion-involving intermolecular modes can be probed, but high enough that the modes are still relatively local compared to those probed by, for example, microwave (dielectric) spectroscopy [2]. THz spectroscopy is sensitive to the motion of cations and their effect on the local water dynamics. In the present work, I have shown the theoretical calculations of Terahertz spectroscopy using molecular dynamics simulation with polarizable AMOEBA forcefield [3]. Our results show that the THz region is mainly governed by the induced dipole moment of the solute and solvent due to the collective dynamics. Unlike polarizable model, non-polarizable forcefields like SPC/E, TIP4P2005 fail to show the THz spectrum around 200 cm-1. Here we have investigated the spectral behaviour for sodium halide solutions in the THz region using AMOEBA forcefield. Due to small concentration of the solute (~1 M) there is little difference in the total spectra. After dissecting the solvation shell region around the halide ions, we have shown that spectral result clearly corresponds to the size and polarizability of the halide ions. This suggests that difference in the THz region of the total spectra might be prominent for the solutes of higher concentration.
References:
1. Heyden, M., Brndermann, E., Heugen, U., Niehues, G., Leitner, D.M. and Havenith, M., J. Am. Chem. Soc., 130, 5773 (2008).
2. Kann, Z. R. and Skinner, J. L. J.Chem. Phys. 144, 234501 (2016).
3. Ponder, J.W., Wu, C., Ren, P., Pande, V.S., Chodera, J.D., Schnieders, M.J., Haque, I., Mobley, D.L., Lambrecht, D.S., DiStasio Jr, R.A. and Head-Gordon,M. J. Phys. Chem. C, 114, 2549 (2010).
a)E-mail: dgautam[at]iitk.ac.in, b)E-mail: amalen[at]iitk.ac.in