Two-response-time model based on CM2/INDO/S2 electrostatic potentials for the dielectric polarization component of solvatochromic shifts on vertical excitation energies

Abstract

ABSTRACT:A model is presented for the electrostatic component of solvatochromic shifts on vertical electronic excitation energies. The model, called vertical electrostatic model 42 (VEM42), is based on representing the solute by a set of distributed atomic monopoles obtained by charge model 2 (CM2) and representing the solvent by its static and optical dielectric constants. The theory is applied here with intermediate neglect of differential overlap for spectroscopy-parameterization 2 (INDO/S2) configuration interaction wave functions. The model is implemented in the ZINDO electronic structure code package. We present illustrative applications to the singlet n → π * excitation of acetone in nine solvents. When the electrostatics are augmented by one-parameter estimates of dispersion and hydrogen-bonding contributions, the experimental solvatochromic shifts in the nine solvents are reproduced with a mean unsigned error of 65 cm −1 (0.2 kcal/mol). These calculations present a compelling picture of the quantitative origin of the solvatochromic red and blue shifts in this prototype n → π * excitation.

QM/MM: what have we learned, where are we, and where do we go from here?

“…We think that it is reasonable to hope that one can do this, if one makes the QM/MM treatment sophisticated enough. For example, one can obtain reasonable values for solvatochromic shifts from continuum solvation models in which the solvent is not treated quantum mechanically [177].…”

Hybrid Monte Carlo simulations of vertical electronic transitions in acetone in aqueous solution

“…1 [19,[34][35][36][37][38][39][40][41][42][43][44][45]. The shifts of the previous studies are in the range 0.14 to 0.38 eV; see Table 7 of Aidas et.al.…”

“…Estimates of dispersion interactions in electronically excited states are difficult to make in explicit solvent models. In fact, it is easier to treat these effects in a macroscopic context; the question how well a macroscopic treatment applies to a microscopic problem remains, however (see discussion by Li et al [19] on this subject for further details and references). In a polar solvent the electrostatic interactions are of greater significance, thus probably making the neglect of the contribution to shift from the dispersion interaction acceptable; in non-polar solvents this may no longer hold [20,21].…”

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

“…They lead to the method 2 quantum mechanical energy in analogy with eq 24 where W 2 EX is the method 2 quantum mechanical energy. Since the application of the variational method does not provide the complete polarization energy contribution, the total energy of the hybrid QM/MM system is (see eq 25) where E pol EX is the polarization energy for the excited state (eq 7). Therefore (see eq 27) Equation 33 contains the explicit polarization response to the excited-state density, unlike method 1 in which no explicit polarization response is added to the excited state.…”

“…There have been some methodological advances for the study of condensed-phase electronic spectroscopy, especially using dielectric continuum methods to represent the solvents. 18,[20][21][22][23][24][25][26][27] While continuum methods are computationally inexpensive, they cannot describe explicit solute-solvent interactions such as hydrogen bonding. In other words, the microscopic structure around the solute molecules is not adequately described by the implicit solvent methods.…”