A study on orientation and absorption spectrum of interfacial molecules by using continuum model

Abstract

In this work, a numerical procedure based on the continuum model is developed and applied to the solvation energy for ground state and the spectral shift against the position and the orientation of the interfacial molecule. The interface is described as a sharp boundary separating two bulk media. The polarizable continuum model (PCM) allows us to account for both electrostatic and nonelectrostatic solute-solvent interactions when we calculate the solvation energy. In this work we extend PCM to the interfacial system and the information about the position and orientation of the interfacial molecule can be obtained. Based on the developed expression of the electrostatic free energy of a nonequilibrium state, the numerical procedure has been implemented and used to deal with a series of test molecules. The time-dependent density functional theory (TDDFT) associated with PCM is used for the electron structure and the spectroscopy calculations of the test molecules in homogeneous solvents. With the charge distribution of the ground and excited states, the position- and orientation-dependencies of the solvation energy and the spectrum have been investigated for the interfacial systems, taking the electrostatic interaction, the cavitation energy, and the dispersion-repulsion interaction into account. The cavitation energy is paid particular attention, since the interface portion cut off by the occupation of the interfacial molecule contributes an extra part to the stabilization for the interfacial system. The embedding depth, the favorable orientational angle, and the spectral shift for the interfacial molecule have been investigated in detail. From the solvation energy calculations, an explanation has been given on why the interfacial molecule, even if symmetrical in structure, tends to take a tilting manner, rather than perpendicular to the interface.

An overview of continuum models for nonequilibrium solvation: Popular theories and new challenge

“…To avoid the inconsistence in the traditional formulations of nonequilibrium solvation, we proposed a solution during the period from 2004 to 2008 for the free energy of nonequilibrium polarization by adopting the Jackson formula for the electrostatic energy increase integral, instead of Eq. , that is, …”

Molecular orientations at interfaces by extended polarizable continuum model

“…The general form for electrostatic free energy under the condition of equilibrium polarization can be given as follows 16, 24: where $\Psi^{\rm sol}$ is the solute wave function in the presence of solvent, H vac the vacuum Hamiltonian, V the polarization potential generated by the induced charge, and V NN the nuclear repulsion energy of the solute. In quantum chemical calculation, G el can be given in a concrete form.…”

“…There have been a number of molecular dynamics simulations 4, 12–14 to study the structure and rotational dynamics of the interface. Some authors used PCM approach to study phase transfer energies 15 and molecular orientation 16, 17. Because of the reaction field of any complex medium can be described with a known Green's function within the framework of integral equation formalism (IEF), diffuse interface 18 was introduced based upon physical intuition.…”

Polarizable continuum model associated with the self-consistent-reaction field for molecular adsorbates at the interface

“…[4][5][6]14,15 Some authors used the polarizable continuum model (PCM) to study phase transfer energies 16 and molecular orientation. 17,18 Relying on the ability of the integral equation formalism (IEF) that describes the reaction field of any complex medium with a known Green's function, diffuse interfaces with position dependent dielectric constants 19 were introduced based upon physical intuition. Those studies demonstrate the applicability of PCM to the interfacial systems.…”

“…In a previous work, 17 we developed an approach to the investigation on the orientation of an interfacial system, based on the dielectric polarizable continuum model (DPCM). 21 However, the procedure in that paper was implemented without considering the mutual polarization between the interfacial molecule and the media.…”