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Ipsen Brewer posted an update 6 months, 3 weeks ago
Hydrophobic solutes significantly alter the water hydrogen bond network. The local alteration of solvation structures gets reflected in the vibrational spectroscopic signal. Although it is possible to detect this microscopic feature by modern infrared spectroscopy, bulk phase spectra often come with a formidable challenge of establishing the connection of experimental spectra to molecular structures. Theoretical spectroscopy can serve as a more powerful tool where spectroscopic data cannot provide the microscopic picture. In the present work, we build a theoretical spectroscopic map based on a hybrid quantum-classical molecular simulation approach using a methane-water system. The single oscillator O-H stretch frequency is well correlated with a collective variable solvation energy. RP-102124 in vivo We construct the spectroscopic maps for fundamental transition frequencies and also the transition dipoles. A bimodal frequency distribution with a blue-shifted population of transition frequency illustrates the presence of gas like water molecules in the hydration shell of methane. This observation is further complemented by a shell-wise decomposition of the O-H stretch frequencies. We observe a significant increase in the ordering of the first solvation water molecules, except those which are directly facing the methane molecule. This is manifested in the redshift of the observed transition frequencies. Temperature dependent simulations depict that the water molecules facing the methane molecule behave similarly to the high temperature water, and a few of the first shell water molecules behave more like cold water.Without rigorous symmetry constraints, solutions to approximate electronic structure methods may artificially break symmetry. In the case of the relativistic electronic structure, if time-reversal symmetry is not enforced in calculations of molecules not subject to a magnetic field, it is possible to artificially break Kramers degeneracy in open shell systems. This leads to a description of excited states that may be qualitatively incorrect. Despite this, different electronic structure methods to incorporate correlation and excited states can partially restore Kramers degeneracy from a broken symmetry solution. For single-reference techniques, the inclusion of double and possibly triple excitations in the ground state provides much of the needed correction. Formally, however, this imbalanced treatment of the Kramers-paired spaces is a multi-reference problem, and so methods such as complete-active-space methods perform much better at recovering much of the correct symmetry by state averaging. Using multi-reference configuration interaction, any additional corrections can be obtained as the solution approaches the full configuration interaction limit. A recently proposed “Kramers contamination” value is also used to assess the magnitude of symmetry breaking.We review recent developments in structural-dynamical phase transitions in trajectory space based on dynamic facilitation theory. An open question is how the dynamic facilitation perspective on the glass transition may be reconciled with thermodynamic theories that posit collective reorganization accompanied by a growing static length scale and, eventually, a vanishing configurational entropy. In contrast, dynamic facilitation theory invokes a dynamical phase transition between an active phase (close to the normal liquid) and an inactive phase, which is glassy and whose order parameter is either a time-averaged dynamic or structural quantity. In particular, the dynamical phase transition in systems with non-trivial thermodynamics manifests signatures of a lower critical point that lies between the mode-coupling crossover and the putative Kauzmann temperature, at which a thermodynamic phase transition to an ideal glass state would occur. We review these findings and discuss such criticality in the context of the low-temperature decrease in configurational entropy predicted by thermodynamic theories of the glass transition.The use of many control variates is proposed as a method to accelerate the second- and third-order Monte Carlo (MC) many-body perturbation (MC-MP2 and MC-MP3) calculations. A control variate is an exactly integrable function that is strongly correlated or anti-correlated with the target function to be integrated by the MC method. Evaluating both integrals and their covariances in the same MC run, one can effect a mutual cancellation of the statistical uncertainties and biases in the MC integrations, thereby accelerating its convergence considerably. Six and thirty-six control variates, whose integrals are known a priori, are generated for MC-MP2 and MC-MP3, respectively, by systematically replacing one or more two-electron-integral vertices of certain configurations by zero-valued overlap-integral vertices in their Goldstone diagrams. The variances and covariances of these control variates are computed at a marginal cost, enhancing the overall efficiency of the MC-MP2 and MC-MP3 calculations by a factor of up to 14 and 20, respectively.Surface plasmon polaritons (SPPs) are propagating waves generated at the interface of a metal (metamaterial) and a dielectric. The intensity of SPPs often exponentially decays away from the surface, while their wavelengths can be tuned by the confinement effect. We present here a computational method based on quantum-mechanical theory to fully describe the interaction between confined SPPs and adsorbed molecules at the interface. Special attention has been paid to the roles of the confinement factor. Taking a prototype dye sensitized solar cell as an example, calculated results reveal that with the increase in the confinement factor in metal/dielectric interfaces, the breakdown of the conventional dipole approximation emerges, which allows efficient harvesting of SPPs with low excitation energies and, thus, increases the efficiency of the solar energy conversion by dye molecules. Furthermore, at the metamaterial/dielectric interface, SPPs with large confinement factors could directly excite the dye molecule from its ground singlet state to the triplet state, opening an entirely new channel with long-living carriers for the photovoltaic conversion. Our results not only provide a rigorous theory for the SPP-molecule interaction but also highlight the important role played by the momentum of the light in plasmon related studies.
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