University of Pretoria
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Semi-empirical supported, Ab Initio derived thermodynamic properties for CℓO2 and its subspecies

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posted on 2023-11-27, 07:21 authored by Natasha MisheerNatasha Misheer

The group of chlorine oxide species comprised of neutral, radical and ionic species (+ve and -ve) including extended compounds, hosting a higher oxygen content, including a number of hydrogen derivatives of CℓO2. Periodic models were constructed using the MedeA-3.3.1 software, followed by a MedeA/VASP (DFT) refinement cycle. Molecular models were prepared with the GaussView-6 model preparation interface of the Gaussian-16 software suite. Conditions applied for all computational studies are presented in this data supplementary document. The empirical pcff+ force field[28], lacked some parameters for a number of these species, in support of Grand Canonical Ensemble simulations and several force field parameters were borrowed and derived from the cvff and pcff force field repositories to complement the pcff+ set, for this purpose. This adjusted pcff+ force field set is presented in Supplementary Tables (S) 2.1–2.7. A bulk (GEMC Ensemble) model approach was devised as an alternative method in determining thermochemical properties. All data sets and conditions can be found in Section S3 of this document. Single monomeric chlorine oxide species were exposed to an isobaric-isothermal GIBBS ensemble (GEMC), applying Grand Canonical Monte Carlo (GCMC) methodology simulations. The optimum ensemble model was extracted and further subjected to Ab Initio VASP-Section 6.2.1 and semi-empirical MOPAC-2016 refinement.

The structures of all the species in this study were first optimised using VASP hybrid Density Functional Theory (DFT) (Section S6) applying the (B3LYP) method and a lower basis set of 6-311G (3df,2p). The optimised structures were then subjected to DFT B3LYP theory, using basis set (cc-pv5z) [32], to determine species energies. It was furthermore required to apply an external calculation step to derive at heats of formation and free energies of formation, from the Gaussian analyses results [27] (Refer: Section-S4.2.1). MOPAC-2016 (Version: 20.302W) was used to compute heats of formation of the single species selected for this study, as well as for the ensemble derived (optimized) models. Conditions used to extract the MOPAC dataset can be found in S4 of this dataset. Thermodynamic properties of the single molecular species (neutral, charged and radical) were obtained applying the following Hamiltonians functionals: AM1, MNDO, MNDOD, PM3, PM6, RM1 and PM7 and is presented in section S5 of this document. VASP-6 was applied to refine the large ensemble models to an acceptable relaxed periodic unit cell status. Single species were exposed to the VASP-6.2.1, MOPAC-2016 and Gaussian-16 software systems, initially to determine their ∆Hf energies (correlated against open literature referenced energies), ultimately to derive their thermochemical properties i.e., Heat Capacities (Cp) and Entropy (S). These properties represented in section S1 were used as prerequisite to derive at chemical reaction schemes, applying standard species-based thermochemistry software FactSage. The FactSage dataset and conditions applied can be found in section S8.




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