Molecular Dynamics Simulations of a Silver Atom in Water: Evidence for a Dipolar Excitonic State (original) (raw)
Related papers
Chemical Physics Letters, 2005
We report mixed quantum-classical molecular dynamics simulations of the optical absorption spectrum of the solvated silver atom and electron in liquid water. The simple one electron model is shown to be able to reproduce the strong temperature dependence of the absorption spectra of hydrated electron as well as the much weaker dependence for the silver atom. A qualitative explanation is provided for this experimental fact. When extending these simulations to very low densities corresponding to supercritical conditions the results display a progressive "desolvation" of the hydrated electron. Two other distinct theoretical models lead to results similar to those of the present QCMD simulations.
Theoretical Study of Neutral Dipolar Atom in Water
Modern Physics Letters B, 2004
We review theoretical studies on the properties of solvated neutral dipolar atoms. The combination use of mixed quantum classical molecular simulations and analytical mean-field dipolar excitonic state theory allows the rationalization of the experimental observations in terms of physical macroscopic properties. A very good agreement is observed between experiments, theory and simulations on the spectroscopic behavior of silver in water. Molecular simulations also give thermodynamic and kinetic information on the reduction reaction of the cation that leads to the neutral atom in an excitonic state.
Ab-initio calculations of Many-Body effects in liquids: the electronic excitations of water
2006
We present ab-initio calculations of the excited state properties of liquid water in the framework of Many-Body Green's function formalism. Snapshots taken from molecular dynamics simulations are used as input geometries to calculate electronic and optical spectra, and the results are averaged over the different configurations. The optical absorption spectra with the inclusion of excitonic effects are calculated by solving the Bethe-Salpeter equation. These calculations are made possible by exploiting the insensitivity of screening effects to a particular configuration. The resulting spectra are strongly modified by many-body effects, both concerning peak energies and lineshapes, and are in good agreement with experiments.
The Journal of Physical Chemistry A, 2003
A molecular dynamics simulation based on ab initio quantum mechanical forces in combination with molecular mechanics has been performed to describe structural and dynamical properties of Ag + in water. The first hydration shell, being the chemically most relevant region, was treated by quantum mechanics at Hartree-Fock level using the LANL2DZ ECP for Ag + and double-plus polarization basis sets for water. The outer region of the system was described using a newly constructed classical three-body corrected potential derived from ab initio energy surfaces. The structure was evaluated in terms of radial and angular distribution functions and coordination number distributions. Water exchange processes between coordination shells have been investigated and evaluated. The results show that the first hydration shell is of rather irregular shape, with an average coordination number of 5.5. Fast water exchange processes between the first and second hydration shell were observed, leading to a preference of 5-and 6-fold coordinated species. The mean residence times of water molecules in the first and second hydration shell are 25 and 10 ps. Because of the labile structure, the librational and vibrational frequencies of first hydration shell ligands are only weakly influenced by the interaction with the ion.
Theoretical Characterisation of the Electronic Excitation in Liquid Water
ChemPhysChem, 2005
Because of its central role in basically all aspects of science, water is certainly one of the most extensively investigated substances, from a theoretical point of view. Many properties have been, in fact, theoretically addressed both in the isolated and condensed phases. Nevertheless, many aspects are still not completely understood and represent the focus of active theoretical interest. Among them, one of the most appealing is certainly the understanding of the electronic properties, in particular the photoabsorption features, in condensed phase. Liquid water experimentally shows, under ambient conditions, the 0-1 absorption maximum at 147 nm, that is, 88 kJ mol À1 shifted toward the blue with respect to the corresponding absorption in vacuum. This blue-shift is known to be more pronounced in ice than in liquid water, and it is also present in small water clusters. From these observations, it is well-established that such a blue-shift is to be mainly ascribed to the short contacts of the excited molecule with its solvation shell (the water dipole moment undergoes an inversion upon 0-1 excitation ). However, only a few theoretical studies have been so far devoted to modelling water photoabsorption in the condensed phase. The computational methods available nowadays are, in fact, able to provide extremely accurate information about the photoexcitation of isolated molecules. However, there are still many difficulties in modelling the same phenomenon in the condensed phase. The inclusion of electronic degrees of freedom (necessary for studying an electronic excitation) into a simulation of a large number of molecules (necessary for a reliable modelling of a condensed phase) is, in fact, still challenging from a computational point of view. In this context, we recently proposed a theoretical computational approach, the perturbed matrix method (PMM), whose main computational feature is the possibility of including, into a classical simulation algorithm, electronic degrees of freedom. In a number [a] M.
Solvation Dynamics in Water: 2. Energy Fluxes on Excited- and Ground-State Surfaces
The journal of physical chemistry. B, 2016
This series' first installment introduced an approach to solvation dynamics focused on expressing the emission frequency shift (following electronic excitation of, and resulting charge change or redistribution in, a solute) in terms of energy fluxes, a work and power perspective. This approach, which had been previously exploited for rotational and vibrational excitation-induced energy flow, has the novel advantage of providing a quantitative view and understanding of the molecular-level mechanisms involved in the solvation dynamics via tracing of the energy flow induced by the electronic excitation's charge change or redistribution in the solute. This new methodology, which was illustrated for the case in which only the excited electronic state surface contributes to the frequency shift (ionization of a monatomic solute in water), is here extended to the general case in which both the excited and ground electronic states may contribute. Simple monatomic solute model variati...
Polarizable force field for molecular dynamics simulations of silver nanoparticles
2019
Contact of silver metal surfaces with water, ions and organic ligands experiences induced charges, leading to attractive polarization. These forces play an important role at inorganic/organic interfaces and complement other non-bonded surface interactions. Despite the importance of these interactions, it, however, remains difficult to implement polarization effects to classical molecular dynamics (MD) simulations. In this contribution, we first present an overview of two popular polarizable models, such as Drude oscillator and the rigid rod model, which are utilized to mimic the polarizability of bulk metals. Second, we implemented the rigid rod model to the polarizable force field (FF) for a silver atom, which was further adapted for atomistic MD simulations of silver nanoparticles (AgNPs) composed of 1397 atoms. In our model, induced charge polarization is represented by the displacement of a charge-carrying virtual site attached rigidly to an original Ag atom. To explore the role...
Physical Review B, 2015
We observe using ab initio methods that localized surface plasmon resonances in icosahedral silver nanoparticles enter the asymptotic region already between diameters of 1 and 2 nm, converging close to the classical quasistatic limit around 3.4 eV. We base the observation on time-dependent density-functional theory simulations of the icosahedral silver clusters Ag 55 (1.06 nm), Ag 147 (1.60 nm), Ag 309 (2.14 nm), and Ag 561 (2.68 nm). The simulation method combines the adiabatic GLLB-SC exchange-correlation functional with real time propagation in an atomic orbital basis set using the projector-augmented wave method. The method has been implemented for the electron structure code GPAW within the scope of this work. We obtain good agreement with experimental data and modeled results, including photoemission and plasmon resonance. Moreover, we can extrapolate the ab initio results to the classical quasistatically modeled icosahedral clusters.