Many body interactions of neutral and charged hydrogen bonded clusters

Water clusters play a pivotal role in many chemical and biological processes. Understanding the molecular-level interactions between water molecules will greatly improve our understanding of these processes. Using high-level ab initio methods, a new classical force field model for water that accurately describes intermolecular interactions has been developed. This force field has been implemented as part of our Drude Model approach to study excess electron interactions with water clusters. The resulting potentials provide a description of neutral and anionic water clusters close to that obtained by much more computationally demanding high-level ab initio electronic structure calculations

Solvent-Induced Shifts in Electronic Spectra of Uracil

Highly accurate excitation spectra are predicted for the low-lying n−π* and π−π* states of uracil for both the gas phase and in water employing the complete active space self-consistent field (CASSCF) and multiconfigurational quasidegenerate perturbation theory (MCQDPT) methods. Implementation of the effective fragment potential (EFP) solvent method with CASSCF and MCQDPT enables the prediction of highly accurate solvated spectra, along with a direct interpretation of solvent shifts in terms of intermolecular interactions between solvent and solute. Solvent shifts of the n−π* and π−π* excited states arise mainly from a change in the electrostatic interaction between solvent and solute upon photoexcitation. Polarization (induction) interactions contribute about 0.1 eV to the solvent-shifted excitation. The blue shift of the n−π* state is found to be 0.43 eV and the red shift of the π−π* state is found to be −0.26 eV. Furthermore, the spectra show that in solution the π−π* state is 0.4 eV lower in energy than the n−π* state

Interfacing the Ab Initio Multiple Spawning Method with Electronic Structure Methods in GAMESS: Photodecay of trans-Azomethane

This work presents a nonadiabatic molecular dynamics study of the nonradiative decay of photoexcited trans-azomethane, using the ab initio multiple spawning (AIMS) program that has been interfaced with the General Atomic and Molecular Electronic Structure System (GAMESS) quantum chemistry package for on-the-fly electronic structure evaluation. The interface strategy is discussed, and the capabilities of the combined programs are demonstrated with a nonadiabatic molecular dynamics study of the nonradiative decay of photoexcited trans-azomethane. Energies, gradients, and nonadiabatic coupling matrix elements were obtained with the state-averaged complete active space self-consistent field method, as implemented in GAMESS. The influence of initial vibrational excitation on the outcome of the photoinduced isomerization is explored. Increased vibrational excitation in the CNNC torsional mode shortens the excited state lifetime. Depending on the degree of vibrational excitation, the excited state lifetime varies from ∼60–200 fs. These short lifetimes are in agreement with time-resolved photoionization mass spectroscopy experiments

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

The simplest variational method for treating electronic excited states, configuration interaction with single excitations (CIS), has been interfaced with the effective fragment potential (EFP) method to provide an effective and computationally efficient approach for studying the qualitative effects of solvents on the electronic spectra of molecules. Three different approaches for interfacing a non-self-consistent field (SCF) excited-state quantum mechanics (QM) method and the EFP method are discussed. The most sophisticated and complex approach (termed fully self consistent) calculates the excited-state electron density with fully self-consistent accounting for the polarization (induction) energy of effective fragments. The simplest approach (method 1) includes a strategy that indirectly adds the EFP perturbation to the CIS wave function and energy via modified Hartree−Fock molecular orbitals, so that there is no direct EFP interaction with the excited-state density. An intermediate approach (method 2) accomplishes the latter in a noniterative perturbative manner. Theoretical descriptions of the three approaches are presented, and test results of solvent-induced shifts using methods 1 and 2 are compared with fully ab initio values. These comparisons illustrate that, at least for the test cases examined here, modification of the ground-state Hartree−Fock orbitals is the largest and most important factor in the calculated solvent-induced shifts. Method 1 is then employed to study the aqueous solvation of coumarin 151 and compared with experimental measurements

Modeling Solvent Effects on Electronic Excited States

The effects of solvents on electronic spectra can be treated efficiently by combining an accurate quantum mechanical (QM) method for the solute with an efficient and accurate method for the solvent molecules. One of the most sophisticated approaches for treating solvent effects is the effective fragment potential (EFP) method. The EFP method has been interfaced with several QM methods, including configuration interaction, time-dependent density functional theory, multiconfigurational methods, and equations-of-motion coupled cluster methods. These combined QM–EFP methods provide a range of efficient and accurate methods for studying the impact of solvents on electronic excited states. An energy decomposition analysis in terms of physically meaningful components is presented in order to analyze these solvent effects. Several factors that must be considered when one investigates solvent effects on electronic spectra are discussed, and several examples are presented

Systems analysis of the effects of the 2014-16 Ebola crisis on WHO-reporting nations’ policy adaptations and 2020-21 COVID-19 response: a systematized review

Abstract Background Recent case studies indicate that the 2014-2016 Ebola outbreak, one of the worst pre-2020 global biological catastrophes in modern history, helped some nations to better prepared their responses for the COVID-19 pandemic. While such national case studies explore how specific nations applied EVD-related policies in their domestic battle against the COVID-19 pandemic, there is no known study that assesses how many WHO nations learned from the West African crisis and to what scale. Objective Applying the policy legacies analytical framework and a systematized literature review, this research examines how prior policy experiences with the 2014-16 EVD crisis as a large-scale emergent outbreak helped to inform and to condition WHO nations to proactively prepare their national policies and health systems for future threats, including ultimately COVID-19. Methods A systematized literature review of 803 evaluated sources assesses to what extent Ebola-affected and non-affected nations directly modified governmental health systems in relation to this warning. The study further evaluates how nations with documented Ebola-related changes fared during COVID-19 compared to nations that did not. We present a categorical theoretical framework that allows for classifying different types of national response activities (termed conditioned learning). Results Ten (90.9%) of 11 nations that were affected by 2014-16 Ebola crisis have documented evidence of repurposing their EVD-related policies to fight COVID-19. 164 (70.0%) of 234 non-EVD-affected nations had documented evidence of specifically adapting national systems to incorporate policy recommendations developed from the 2014-16 crisis, which informed their COVID-19 responses in 2020. Conclusions The shock of 2014-16 EVD outbreak affected most nations around the world, whether they experienced Ebola cases. We further develop a categorical framework that helps characterised nations previous experiences with this biological catastrophe, providing a means to analyse to what extent that individual nations learned and how these EVD-related changes helped inform their COVID-19 response. Nations that demonstrated EVD-related conditioned learning nations tended to have more stringent COVID-19 responses before April 2020 and utilized documented response mechanisms developed out of the West African crisis

Solvent-Induced Shifts in Electronic Spectra of Uracil

Highly accurate excitation spectra are predicted for the low-lying n−π* and π−π* states of uracil for both the gas phase and in water employing the complete active space self-consistent field (CASSCF) and multiconfigurational quasidegenerate perturbation theory (MCQDPT) methods. Implementation of the effective fragment potential (EFP) solvent method with CASSCF and MCQDPT enables the prediction of highly accurate solvated spectra, along with a direct interpretation of solvent shifts in terms of intermolecular interactions between solvent and solute. Solvent shifts of the n−π* and π−π* excited states arise mainly from a change in the electrostatic interaction between solvent and solute upon photoexcitation. Polarization (induction) interactions contribute about 0.1 eV to the solvent-shifted excitation. The blue shift of the n−π* state is found to be 0.43 eV and the red shift of the π−π* state is found to be −0.26 eV. Furthermore, the spectra show that in solution the π−π* state is 0.4 eV lower in energy than the n−π* state.This article is from Journal of Physical Chemistry A 115 (2011): 4574, doi:10.1021/jp112230f. </p

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

The simplest variational method for treating electronic excited states, configuration interaction with single excitations (CIS), has been interfaced with the effective fragment potential (EFP) method to provide an effective and computationally efficient approach for studying the qualitative effects of solvents on the electronic spectra of molecules. Three different approaches for interfacing a non-self-consistent field (SCF) excited-state quantum mechanics (QM) method and the EFP method are discussed. The most sophisticated and complex approach (termed fully self consistent) calculates the excited-state electron density with fully self-consistent accounting for the polarization (induction) energy of effective fragments. The simplest approach (method 1) includes a strategy that indirectly adds the EFP perturbation to the CIS wave function and energy via modified Hartree−Fock molecular orbitals, so that there is no direct EFP interaction with the excited-state density. An intermediate approach (method 2) accomplishes the latter in a noniterative perturbative manner. Theoretical descriptions of the three approaches are presented, and test results of solvent-induced shifts using methods 1 and 2 are compared with fully ab initio values. These comparisons illustrate that, at least for the test cases examined here, modification of the ground-state Hartree−Fock orbitals is the largest and most important factor in the calculated solvent-induced shifts. Method 1 is then employed to study the aqueous solvation of coumarin 151 and compared with experimental measurements.Reprinted (adapted) with permission from Journal of Physical Chemistry a 114 (2010): 6742, doi:10.1021/jp101780r. Copyright 2010 American Chemical Society.</p