Combined Multireference Configuration Interaction/ Molecular Dynamics Approach for Calculating Solvatochromic Shifts:  Application to then_O→ π* Electronic Transition of Formaldehyde

Abstract

A combined quantum mechanics/molecular mechanics method is described here for considering the solvatochromic shift of excited states in solution. The quantum mechanical solute is described using high level multireference configuration interaction methods (MRCI), while molecular dynamics is used for obtaining the structure of the solvent around the solute. The electrostatic effect of the solvent is included in the quantum description of the solute in an averaged way. This method is used to study solvent effects on the n(O) --> pi* electronic transition of formaldehyde in aqueous solution. The effects of solute polarization, basis sets, and dynamical correlation on the solvatochromic shift, and on dipole moments, have been investigated.

Communication: Constructing an implicit quantum mechanical/molecular mechanics solvent model by coarse-graining explicit solvent

“…Mean-field models such as the averaged solvent electrostatic potential (ASEP) and related methods embed the system in point charges obtained by averaging over many solvent configurations. [1][2][3][4][5] Integral equation theories such as the reference interaction site model (RISM) also provide a useful means of obtaining information about the statistical structure and properties of the solvent. 6 Alternatively, one can pre-compute the response of the solute to the solvent and use that in place of QM calculations during the a) Present address: Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.…”

Implementation of the analytic energy gradient for the combined time-dependent density functional theory/effective fragment potential method: Application to excited-state molecular dynamics simulations

“…The excitation energy difference between the gas and solution phases, the solvatochromic shift, is calculated to be 0.34 eV, which is comparable to the experimental value of 0.21 eV for acetone 56 as well as to previous theoretical results. 20,[34][35][36][37][38][39][40][41][42] …”

“…Although there are no experimental fluorescence spectra available for aqueous formaldehyde, this solute-solvent system has been the subject of several theoretical studies. 20,21,[33][34][35][36][37][38][39][40][41][42][43][44][45] The ultimate goal is to apply the TDDFT/EFP1 method to large-scale QM/MM simulations in excited states. Therefore, the present study on this simple system is an initial step toward applications to more complex systems.…”

Solvent-Induced Frequency Shifts: Configuration Interaction Singles Combined with the Effective Fragment Potential Method

“…Some studies have considered the importance of mutual solute-solvent polarization between solute and solvent molecules on the excitation energy. 46,50,51 Xu et al examined the effects of solute polarization of the n-π* transition of formaldehyde in the condensed phase using a QM/ MM method that combines MRCI and molecular dynamics simulations using a classical force field. 46 They found that the solute polarizability is an important component of solventinduced shifts of formaldehyde, contributing about 35% of the shift in the calculated excitation energy.…”

“…46,50,51 Xu et al examined the effects of solute polarization of the n-π* transition of formaldehyde in the condensed phase using a QM/ MM method that combines MRCI and molecular dynamics simulations using a classical force field. 46 They found that the solute polarizability is an important component of solventinduced shifts of formaldehyde, contributing about 35% of the shift in the calculated excitation energy. Aidas et al have found that the inclusion of explicit polarization due to solvent molecules in combined quantum mechanics/molecular mechanics (QM/MM) calculations of excited states slightly lowers the excitation energy.…”