1,077 research outputs found
Acceleration of Solvation Free Energy Calculation via Thermodynamic Integration Coupled with Gaussian Process Regression and Improved Gelman-Rubin Convergence Diagnostics
The determination of the solvation free energy of ions and molecules holds
profound importance across a spectrum of applications spanning chemistry,
biology, energy storage, and the environment. Molecular dynamics simulations
are a powerful tool for computing this critical parameter. Nevertheless, the
accurate and efficient calculation of solvation free energy becomes a
formidable endeavor when dealing with complex systems characterized by potent
Coulombic interactions and sluggish ion dynamics and, consequently, slow
transition across various metastable states. In the present study, we expose
limitations stemming from the conventional calculation of the statistical
inefficiency g in the thermodynamic integration method, a factor that can
hinder the determination of convergence of the solvation free energy and its
associated uncertainty. Instead, we propose a robust scheme based on
Gelman-Rubin convergence diagnostics. We leverage this improved estimation of
uncertainties to introduce an innovative accelerated thermodynamic integration
method based on Gaussian Process regression. This methodology is applied to the
calculation of the solvation free energy of trivalent rare earth elements
immersed in ionic liquids, a scenario where the aforementioned challenges
render standard approaches ineffective. The proposed method proves effective in
computing solvation free energy in situations where traditional thermodynamic
integration methods fall short.Comment: Main text: 24 pages, 8 figures; Supporting information: 8 pages, 9
figures, 2 table
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Theoretical studies in the stability of molecular platinum catalysts for hydrogen production
Effect of Intra-molecular Disorder and Inter-molecular Electronic Interactions on the Electronic Structure of Poly-p-Phenylene Vinylene (PPV)
We investigate the role of intra-molecular conformational disorder and
inter-molecular electronic interactions on the electronic structure of disorder
clusters of poly-p-phenylene vinylene (PPV) oligomers. Classical molecular
dynamics is used to determine probable molecular geometries, and
first-principle density functional theory (DFT) calculations are used to
determine electronic structure. Intra-molecular and inter-molecular effects are
disentangled by contrasting results for densely packed oligomer clusters with
those for ensembles of isolated oligomers with the same intra-molecular
geometries. We find that electron trap states are induced primarily by
intra-molecular configuration disorder, while the hole trap states are
generated primarily from inter-molecular electronic interactions.Comment: 4 pages, 4 figures. Compile with pdflate
Catalyst-Inspired Charge Carriers for High Energy Density Redox Flow Batteries
We introduce a theoretical design approach aiming at improving energy density of redox flow batteries (RFBs) via the utilization of redox non-innocent ligands capable of stabilizing a metal center in a wide range of oxidation states. Our findings suggest that this promotes the possibility of multiple redox events as well as high open circuit voltages. Specifically, we have proposed two Fe-coordination complexes (I, Fe(Me2Pytacn)(C2N3H2), and II, Fe(H2pmen)(C2N3H2)) combining two different types of ligands, i.e., catalyst-inspired scaffolds and triazole ring, which were previously shown to promote high and low oxidation states in transition metals, respectively. These complexes exhibit as many as six theoretical redox events in the full range of charge states +4 → −2, several of which reside within the electrochemical window of acetonitrile. Electronic structure calculations show that the Fe center exhibits oxidation states ranging from the very rare Fe4+ to Fe1+. Values of the reduction potentials as well as nature of the redox events of both complexes is found to be similar in their high +4 → +1 charge states. In contrast, while exhibiting qualitatively similar redox behavior in the lower 0 → −2 range, some differences in the electronic ground states, delocalization patterns as well as reduction potential values are also observed. The calculated open circuit voltages can reach values of 5.09 and 6.14 V for complexes I and II, respectively, and hold promise to be experimentally accessible within the electrochemical window of acetonitrile expanded by addition of ionic liquids. The current results obtained for these two complexes are intended to illustrate a more general principle based on the simultaneous utilization of two types of ligands responsible for the stabilization of high and low oxidation states of the metal that can be used to design the next-generation charge carriers capable of supporting multi-electron redox and operating in a broad range of charge states, leading to RFBs with greater energy density
Effect of spin-orbit coupling on the actinide dioxides AnO2 (An=Th, Pa, U, Np, Pu, and Am): A screened hybrid density functional study
We present a systematic comparison of the lattice structures, electronic density of states, and band gaps of actinide dioxides, AnO2 (An=Th, Pa, U, Np, Pu, and Am) predicted by the Heyd-Scuseria-Ernzerhof screened hybrid density functional (HSE) with the self-consistent inclusion of spin-orbit coupling (SOC). The computed HSE lattice constants and band gaps of AnO2 are in consistently good agreement with the available experimental data across the series, and differ little from earlier HSE results without SOC. ThO2 is a simple band insulator (f 0), while PaO2, UO2, and NpO2 are predicted to be Mott insulators. The remainders (PuO2 and AmO2) show considerable O2p/An5f mixing and are classified as charge-transfer insulators. We also compare our results for UO2, NpO2, and PuO2 with the PBE+U, self interaction correction (SIC), and dynamic mean-field theory (DMFT) many-body approximations
Complexation and Redox Chemistry of Neptunium, Plutonium and Americium with a Hydroxylaminato Ligand
Plutonium coordination and redox chemistry with the CyMe4-BTPhen polydentate N-donor extractant ligand
Complexation of Pu(IV) with the actinide extractant CyMe4-BTPhen (2,9-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-1,10-phenanthroline) was followed by vis-NIR spectroscopy in acetonitrile solution. The solid-state structure of the crystallized product suggests that Pu(IV) is reduced to Pu(III) upon complexation. Analysis by DFT modeling is consistent with metal-based rather than ligand-based reduction
Unpredictability in seasonal infectious diseases spread
In this work, we study the unpredictability of seasonal infectious diseases
considering a SEIRS model with seasonal forcing. To investigate the dynamical
behaviour, we compute bifurcation diagrams type hysteresis and their respective
Lyapunov exponents. Our results from bifurcations and the largest Lyapunov
exponent show bistable dynamics for all the parameters of the model. Choosing
the inverse of latent period as control parameter, over 70% of the interval
comprises the coexistence of periodic and chaotic attractors, bistable
dynamics. Despite the competition between these attractors, the chaotic ones
are preferred. The bistability occurs in two wide regions. One of these regions
is limited by periodic attractors, while periodic and chaotic attractors bound
the other. As the boundary of the second bistable region is composed of
periodic and chaotic attractors, it is possible to interpret these critical
points as tipping points. In other words, depending on the latent period, a
periodic attractor (predictability) can evolve to a chaotic attractor
(unpredictability). Therefore, we show that unpredictability is associated with
bistable dynamics preferably chaotic, and, furthermore, there is a tipping
point associated with unpredictable dynamics
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