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Computational Chemistry Assisted Simulation for Metal Ion Separation in the Aqueous-Organic Biphasic Systems
Published in Jayant K. Singh, Nishith Verma, Aqueous Phase Adsorption, 2018
Sk. Musharaf Ali, Anil Boda, Ashish Kumar Singha Deb, Pooja Sahu
Density functional theory-based electronic structure calculations have been shown to be very useful in interpreting the coordinating environment of different radionuclide towards ligands. The interaction strength of extractant molecules with the radionuclide can be decisively predicted and thus can be used as a prescreening criteria. The preferential selectivity of radionuclide towards a particular extractant can be well predicted by determining the free energy of extraction using thermodynamic cycle, which is correlated with the experimentally determined distribution constants as confirmed by determining the free energy of UO22+ and Pu4+ towards DH2EHA, DHOA, TMDGA, and GO-EGMP. COSMO solvation model can be authoritatively used for the calculation of structural and thermodynamic properties in the solution phase. Even the diluents for solvent extraction can be screened using DFT-COSMO combination. It can be stated that the DFT-based computational methods have played and are still playing a key role in understanding the separation mechanism of Am3+-Eu3+ ions from nuclear waste with varieties of extractants. In addition, high-fidelity MDsimulations were shown to capture the experimentally observed migration of uranyl nitrate from the aqueous to the organic phase. MD simulations on several systems involving various acid models reveal the effect of acid in the aqueous phase, organic phase, and at the interface. Simulations with varied TBP and acid concentration yield the trends similar to experiments and thus are helpful in planning the experiments.
Li -Ion Battery Materials and Electrolytes
Published in Aneeya Kumar Samantara, Satyajit Ratha, Electrochemical Energy Conversion and Storage Systems for Future Sustainability, 2020
In the quantum chemical simulations, the electrolytic solvents are represented by the two solvation models; implicit solvent model and explicit solvent model (Bryantsev, 2012; Marenich et al., 2009; Rayne et al., 2010). The basis of the implicit continuum model is the sharp boundary between the solute and the bulk of the solvent, represented as a structure-less polarizable medium, characterized by its dielectric constant (Tomasi et al., 2005). In these models, the molecule/cluster under investigation is located inside a cavity surrounded by a homogeneous dielectric medium of the solvents such as; acetonitrile (MeCN, ε = 35.6), EC (ε = 89.6), propylene carbonate (PC, ε = 64.0), Diethylene carbonate (DEC, ε = 2.40), DMC (ε = 7.15) and Triethylene glycol dimethyl ether (Triglime, ε = 7.94). The implicit solvent model has been successfully applied in the investigation of the chemical reaction within the surrounding medium (Kushwaha et al., 2017, 2018; Kushwaha and Nayak, 2017), There are several continuum models has proposed for expressing the solvent media, out of which polarizable continuum model (PCM) is generally used to represent continuum dielectric medium. Mathematically, the PCM is expressed by the Poisson-Boltzmann equation which is an expansion term of Poisson’s equation. Recently solvation model on density (SMD) is getting much attention for solvation model (Marenich et al., 2009). Similar to the PCM, the SMD model solve the Poisson-Boltzmann equation analytically, only difference is that SMD model used specific parameterize radii for the construction of cavity. The conductor boundary condition based COSMO solvation model is also an implicit solvent model (Klamt and Schüürmann, 1993). The computational cost calculation using the implicit model is lower in comparison to others while is does not maintain the high accuracy especially reaction mechanism. In the explicit solvation model, the molecular solvents form the solvation shell (changes during transfer between the electrodes) around the Li+ ion, either in the electrolyte or at the electrode interfaces. For example, in the case of EC, the coordination number of Li+ has been found to be four, which reduces at the interfaces (Bhatt et al., 2012; Bhatt and O’Dwyer, 2014; Cui et al., 2016). The explicit solvent model provides the more realistic picture of the solute-solvent interaction in comparison to implicit solvent model. Although the computational cost is the major drawback of the explicit solvent model.
Interfacial tension in water/n-decane/naphthenic acid systems predicted by a combined COSMO-RS theory and pendant drop experimental study
Published in Molecular Physics, 2020
Kristian B. Olesen, Anne-Sofie Dahl Pedersen, Lasse V. Nikolajsen, Martin P. Andersson, Theis I. Sølling, Stephan P. A. Sauer, Kurt V. Mikkelsen
The COnductor-like Screening Model for Real Solvents (COSMO-RS) solvation theory is an extension to the COnductor-like Screening Model (COSMO) dielectric continuum model. The COSMO solvation model assumes that the solute is embedded in a conductor representing the solvent. This greatly simplifies the calculation of the screening charge densities acting onto the segmented molecular surface using computational methods [15]. COSMO-RS uses this idealised solvation state as a reference state. Fluids are then treated as ensembles of pairwise interacting surface segments that have a surface charge density. The composition of an ensemble is determined by the molecular composition of the fluid and the screening charge densities of the surface segments of the molecules in the fluid [16]. Applying statistical thermodynamics to this ensemble allows for the calculation of chemical potentials of solutes in solvents relative to the ideally screened reference state [17]. From the chemical potential, the two-phase partitioning of solutes, and solvation energies amongst others can be calculated. COSMO-RS calculates energies relative to the reference state using only inputs from the original quantum mechanical calculation. Thus, COSMO-RS calculations can be performed using maximum two DFT calculations for each species in the system (gas + conductor reference state).