Atomistic simulations of a solid/liquid interface: a combined force field and first principles approach to the structure and dynamics of acetonitrile near an anatase surface

Abstract

Atomistic simulations of a solid/liquid interface: a combined force field and first principles approach to the structure and dynamics of acetonitrile near an anatase surface Schiffmann, F; Hutter, J; VandeVondele, J Schiffmann, F;Hutter, J; VandeVondele, J (2008). Atomistic simulations of a solid/liquid interface: a combined force field and first principles approach to the structure and dynamics of acetonitrile near an anatase surface. Atomistic simulations of a solid/liquid interface: a combined force field and first principles approach to the structure and dynamics of acetonitrile near an anatase surface AbstractThe acetonitrile/anatase(101) interface can be considered a prototypical interface between an oxide and a polar aprotic liquid, and is common in dye sensitized solar cells. Using first principles molecular dynamics simulations of a slab of TiO2 in contact with neat acetonitrile (MeCN), the liquid structure near this interface has been characterized. Furthermore, in order to investigate properties that require extensive sampling, a classical force field to describe the MeCN/TiO2 interaction has been optimized, and we show that this force field accurately describes the structure near the interface. We find a surprisingly strong interaction of MeCN with TiO2, which leads to an ordered first MeCN layer displaying a significantly enhanced molecular dipole. The strong dipolar interactions between solvent molecules lead to pronounced layering further away from the interface, each successive layer having an alternate orientation of the molecular dipoles. At least seven distinct solvent layers (approximately 12 angstrom) can be discerned in the orientational distribution function. The observed structure also strongly suppresses diffusion parallel to the interface in the first nanometer of the liquid. These results show that the properties of the liquid near the interface differ from those in the bulk, which suggests that solvation near the interface will be distinctly different from solvation in the bulk.Atomistic simulations of a solid/liquid interface: A combined force field and first principles approach to the structure and dynamics of acetonitrile near an anatase surface Abstract.The acetonitrile / anatase(101) interface can be considered a prototypical interface between an oxide and a polar aprotic liquid, and is common in dye sensitized solar cells. Using first principles molecular dynamics simulations of a slab of TiO 2 in contact with neat acetonitrile (MeCN), the liquid structure near this interface has been characterized. Furthermore, in order to investigate properties that require extensive sampling, a classical force field to describe the MeCN/TiO 2 interaction has been optimized, and we show that this force field accurately describes the structure near the interface. We find a surprisingly strong interaction of MeCN with TiO 2 , which leads to an ordered first MeCN layer displaying a significantly enhanced molecular dipole. The strong dipolar interactions between solvent molecules lead to pronounc...

An atomistic picture of the regeneration process in dye sensitized solar cells

“…The observed structure can therefore not be attributed to a correlation between ions, but must be induced by the solvent. In previous work, we have observed a strong layering of the acetonitrile near the anatase(101) surface, due to a favorable interaction of the nitrile group with the titanium atoms of the surface, and the pronounced dipolar nature of the solvent (14). Here, we observe that the structure of the liquid, as illustrated with a density profile in Fig.…”

“…The plane wave density cutoff was set to 280 Ry. The FF for acetonitrile is based on point charges, van der Waals interactions and harmonic bonded terms as found in literature (21), TiO 2 was modeled using point charges, and a Buckingham potential from literature (22), while the interaction between both species has been derived and validated against ab initio data in our earlier work (14). Parameters for the cations have been taken from literature (23,24), for fluoride we employed σ ¼ 2.90 Å and ϵ ¼ 0.105 kJ∕mol, for chloride σ ¼ 4.04 Å and ϵ ¼ 0.157 kJ∕mol, for iodide σ ¼ 4.60 Å and ϵ ¼ 0.438 kJ∕mol similar to ref.…”

Real-World Predictions from Ab Initio Molecular Dynamics Simulations

“…The authors also carried out in situ vibrational spectroscopy and could thus confirm the reversible binding of I 2 to the thiocyanate group. Furthermore, Schiffmann et al were able to simulate the electrolyte near the interface and found that acetonitrile is able to cover the (101) surface of anatase with a passivating layer that inhibits direct contact of the redox mediator with the oxide [229,230]. It was also observed that the solvent structure specifically enhances the concentration of I À at a distance which further favors rapid dye regeneration.…”

Influence of a nearby substrate on the reorganization energy of hole exchange between dye molecules

“…However statistically relevant calculations based on MD are computationally prohibitive 4 and force fields cannot, to this date, provide a satisfactory atomistic description of the interactions between mixed phase systems. 20 Density Functional Theory (DFT) calculations of the charge donor/acceptor coupled with a continuum model for the surroundings is an attractive alternative. Small inhomogeneities in the medium can be accounted for using dielectric mixing theory 21 and recent development of the Polarizable Continuum Model (PCM) allows anisotropic media to be implemented (i.e.…”