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1. Full optical rotation tensor at coupled cluster with single and double excitations level in the modified velocity gauge

   https://doi.org/10.1002/chir.23310  

   Zhang, Kaihua; Balduf, Ty; Caricato, Marco (April 2021, Chirality)

   Abstract This work presents the first simulations of the full optical rotation (OR) tensor at coupled cluster with single and double excitations (CCSD) level in the modified velocity gauge (MVG) formalism. The CCSD‐MVG OR tensor is origin independent, and each tensor element can in principle be related directly to experimental measurements on oriented systems. We compare the CCSD results with those from two density functionals, B3LYP and CAM‐B3LYP, on a test set of 22 chiral molecules. The results show that the functionals consistently overestimate the CCSD results for the individual tensor components and for the trace (which is related to the isotropic OR), by 10%–20% with CAM‐B3LYP and 20%–30% with B3LYP. The data show that the contribution of the electric dipole–magnetic dipole polarizability tensor to the OR tensor is on average twice as large as that of the electric dipole–electric quadrupole polarizability tensor. The difficult case of (1S,4S)‐(–)‐norbornenone also reveals that the evaluation of the former polarizability tensor is more sensitive than the latter. We attribute the better agreement of CAM‐B3LYP with CCSD to the ability of this functional to better reproduce electron delocalization compared with B3LYP, consistent with previous reports on isotropic OR. The CCSD‐MVG approach allows the computation of reference data of the full OR tensor, which may be used to test more computationally efficient approximate methods that can be employed to study realistic models of optically active materials. 

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2. A Fermi resonance and a parallel-proton-transfer overtone in the Raman spectrum of linear centrosymmetric N4H+: A polarizability-driven first principles molecular dynamics study

   https://doi.org/10.1063/5.0119251  

   Omodemi, Oluwaseun; Revennaugh, Ramsay; Riley, Janiyah; Kaledin, Alexey L.; Kaledin, Martina (October 2022, The Journal of Chemical Physics)

   We present molecular dynamics (MD), polarizability driven MD (α-DMD), and pump–probe simulations of Raman spectra of the protonated nitrogen dimer N4H+, and some of its isotopologues, using the explicitly correlated coupled-cluster singles and doubles with perturbative triples [CCSD(T)]-F12b/aug-cc-pVTZ based potential energy surface in permutationally invariant polynomials (PIPs) of Yu et al. [J. Phys. Chem. A 119, 11623 (2015)] and a corresponding PIP-derived CCSD(T)/aug-cc-pVTZ-tr (N:spd, H:sp) polarizability tensor surface (PTS), the latter reported here for the first time. To represent the PTS in terms of a PIP basis, we utilize a recently described formulation for computing the polarizability using a many-body expansion in the orders of dipole–dipole interactions while generating a training set using a novel approach based on linear regression for potential energy distributions. The MD/α-DMD simulations reveal (i) a strong Raman activity at 260 and 2400 cm−1, corresponding to the symmetric N–N⋯H bend and symmetric N–N stretch modes, respectively; (ii) a very broad spectral region in the 500–2000 cm−1 range, assignable to the parallel N⋯H+⋯N proton transfer overtone; and (iii) the presence of a Fermi-like resonance in the Raman spectrum near 2400 cm−1 between the Σg+ N–N stretch fundamental and the Πu overtone corresponding to perpendicular N⋯H+⋯N proton transfer. 

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3. Tight bounds correlating peak absorption with Q-factor in composites and metallic clusters of particles

   https://doi.org/10.1063/5.0155092  

   Deshmukh, Kshiteej J.; Milton, Graeme W. (August 2023, Applied Physics Letters)

   Resonances are fundamentally important in the field of nano-photonics and optics. Thus, it is of great interest to know what are the limits to which they can be tuned. The bandwidth of the resonances in materials is an important feature, which is commonly characterized by using the Q-factor. We present tight bounds correlating the peak absorption with the Q-factor of two-phase quasi-static metamaterials and plasmonic resonators evaluated at a given peak frequency by introducing an alternative definition for the Q-factor in terms of the complex effective permittivity of the composite material. This composite may consist of well-separated clusters of plasmonic particles, and, thus, we obtain bounds on the response of a single cluster as governed by the polarizability. Optimal metamaterial microstructure designs achieving points on the bounds are presented. The most interesting optimal microstructure is a limiting case of doubly coated ellipsoids that attains points on the lower bound. We also obtain bounds on Q for three dimensional, isotropic, and fixed volume fraction two-phase quasi-static metamaterials and particle clusters with an isotropic polarizability. Some almost optimal isotropic microstructure geometries are identified. 

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4. Thermal Transport in Citrate-Capped Gold Interfaces Using a Polarizable Force Field

   https://doi.org/10.1021/acs.jpcc.2c01333  

   Shavalier, Sydney A.; Gezelter, J. Daniel (January 2022, The Journal of Physical Chemistry C)

   The interfacial thermal conductance from solvated gold nanostructures capped with sodium citrate was determined using reverse nonequilibrium molecular dynamics (RNEMD) methods. The surfaces of spherical nanoparticles and the (111) surfaces of fcc gold slabs were modeled using the density readjusting-embedded atom method (DR-EAM) as well as with the standard embedded atom method (EAM), and the effects of polarizability on the binding preferences of citrate were determined. We find that the binding configurations of citrate depend significantly on gold surface curvature and are not strongly influenced by surface polarizability. The interfacial thermal conductance was also determined for the spherical nanoparticles and (111) surfaces, and we find that applying DR-EAM increases the interfacial thermal conductance for systems with spherical nanoparticles much more sharply than for systems with (111) surfaces. Through analysis of excess charge density near the interface, we find that inclusion of polarizability has a larger impact on image charge creation in nanospheres than it does for the planar (111) interfaces. This effectively increases the interaction strength to polar species in the solvent, yielding larger interfacial thermal conductance estimates for the nanospheres. 

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5. A predictive model for salt nanoparticle formation using heterodimer stability calculations

   https://doi.org/10.5194/acp-21-11637-2021  

   Chee, Sabrina; Barsanti, Kelley; Smith, James N.; Myllys, Nanna (January 2021, Atmospheric Chemistry and Physics)

   null (Ed.)

   Abstract. Acid–base clusters and stable salt formation are critical drivers of new particle formation events in the atmosphere. In this study, we explore salt heterodimer (a cluster of one acid and one base) stability as a function of gas-phase acidity, aqueous-phase acidity, heterodimer proton transference, vapor pressure, dipole moment and polarizability for salts comprised of sulfuric acid, methanesulfonic acid and nitric acid with nine bases. The best predictor of heterodimer stability was found to be gas-phase acidity. We then analyzed the relationship between heterodimer stability and J4×4, the theoretically predicted formation rate of a four-acid, four-base cluster, for sulfuric acid salts over a range of monomer concentrations from 105 to 109 molec cm−3 and temperatures from 248 to 348 K and found that heterodimer stability forms a lognormal relationship with J4×4. However, temperature and concentration effects made it difficult to form a predictive expression of J4×4. In order to reduce those effects, heterodimer concentration was calculated from heterodimer stability and yielded an expression for predicting J4×4 for any salt, given approximately equal acid and base monomer concentrations and knowledge of monomer concentration and temperature. This parameterization was tested for the sulfuric acid–ammonia system by comparing the predicted values to experimental data and was found to be accurate within 2 orders of magnitude. We show that one can create a simple parameterization that incorporates the dependence on temperature and monomer concentration on J4×4 by defining a new term that we call the normalized heterodimer concentration, Φ. A plot of J4×4 vs. Φ collapses to a single monotonic curve for weak sulfate salts (difference in gas-phase acidity >95 kcal mol−1) and can be used to accurately estimate J4×4 within 2 orders of magnitude in atmospheric models. 

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