124 research outputs found
Solvation in atomic liquids: connection between Gaussian field theory and density functional theory
For the problem of molecular solvation, formulated as a liquid submitted to
the external potential field created by a molecular solute of arbitrary shape
dissolved in that solvent, we draw a connection between the Gaussian field
theory derived by David Chandler [Phys. Rev. E, 1993, 48, 2898] and classical
density functional theory. We show that Chandler's results concerning the
solvation of a hard core of arbitrary shape can be recovered by either
minimising a linearised HNC functional using an auxiliary Lagrange multiplier
field to impose a vanishing density inside the core, or by minimising this
functional directly outside the core --- indeed a simpler procedure. Those
equivalent approaches are compared to two other variants of DFT, either in the
HNC, or partially linearised HNC approximation, for the solvation of a
Lennard-Jones solute of increasing size in a Lennard-Jones solvent. Compared to
Monte-Carlo simulations, all those theories give acceptable results for the
inhomogeneous solvent structure, but are completely out-of-range for the
solvation free-energies. This can be fixed in DFT by adding a hard-sphere
bridge correction to the HNC functional.Comment: 14 pages, 4 figure
Quantized time correlation function approach to non-adiabatic decay rates in condensed phase: Application to solvated electrons in water and methanol
A new, alternative form of the golden rule formula defining the non-adiabatic transition rate between two quantum states in condensed phase is presented. The formula involves the quantum time correlation function of the energy gap, of the non-adiabatic coupling, and their cross terms. Those quantities can be inferred from their classical counterparts, determined via MD simulations. The formalism is applied to the problem of the non-adiabatic relaxation of an equilibrated p-electron in water and methanol. We find that, in both solvent, the relaxation is induced by the coupling to the vibrational modes and the quantum effects modify the rate by a factor of 2-10 depending on the quantization procedure applied. The resulting p-state lifetime for a hypothetical equilibrium excited state appears extremely short, in the sub-100 fs regime. Although this result is in contrast with all previous theoretical predictions, we also illustrate that the lifetimes computed here are very sensitive to the simulated electronic quantum gap and to the strongly correlated non-adiabatic coupling
Ammoniated electron as a solvent stabilized multimer radical anion
The excess electron in liquid ammonia ("ammoniated electron") is commonly
viewed as a cavity electron in which the s-type wave function fills the
interstitial void between 6-9 ammonia molecules. Here we examine an alternative
model in which the ammoniated electron is regarded as a solvent stabilized
multimer radical anion, as was originally suggested by Symons [Chem. Soc. Rev.
1976, 5, 337]. In this model, most of the excess electron density resides in
the frontier orbitals of N atoms in the ammonia molecules forming the solvation
cavity; a fraction of this spin density is transferred to the molecules in the
second solvation shell. The cavity is formed due to the repulsion between
negatively charged solvent molecules. Using density functional theory
calculations for small ammonia cluster anions in the gas phase, it is
demonstrated that such core anions would semi-quantitatively account for the
observed pattern of Knight shifts for 1-H and 14-N nuclei observed by NMR
spectroscopy and the downshifted stretching and bending modes observed by
infrared spectroscopy. It is speculated that the excess electrons in other
aprotic solvents (but not in water and alcohols) might be, in this respect,
analogous to the ammoniated electron, with substantial transfer of the spin
density into the frontier N and C orbitals of methyl, amino, and amide groups
forming the solvation cavity.Comment: 34 pages, 12 figures; to be submitted to J Phys Chem
De la phase gazeuse à la phase liquide
Conférence du 28 Août au 2 Septembre 2005. Communication par affiche
Quantized time correlation function approach to nonadiabatic decay rates in condensed phase
Conférence du 14 au 16 mars 2005. Communication par affiche
Dynamique moléculaire: explorer un ensemble thermodynamique avec des trajectoires
Conférence du 6 au 10 Juin 2005. Communication par affiche
Quantized time correlation function approach to nonadiabatic decay rates in condensed phase: Application to solvated electrons in water and in methanol
Conférence du 18 au 20 Mai 2005. Communication par affiche
Coarse grained models of solvent and proteins
Conférence du 4 au 6 Décembre 2005. Communication par affiche
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