145 research outputs found
Comment on phase-space representation of quantum state vectors
A simple approach to phase-space representation of quantum state vectors using the displacement-operator formalism is presented. Although the resulting expressions for the fundamental operators (position and momentum) are equivalent to those obtained by other methods, this approach provides both alternative mathematical foundation as well as physical interpretation of phase-space representation of quantum state vectors
Excited-State Solvation Structure of Transition Metal Complexes from Molecular Dynamics Simulations and Assessment of Partial Atomic Charge Methods
In this work, we investigate the excited-state solute and solvation structure
of , ,
and
(bpy=2,2'-pyridine; bmip=2,6-bis(3-methyl-imidazole-1-ylidine)-pyridine;
phen=1,10-phenanthroline) transition metal complexes (TMCs) in terms of
solute-solvent radial distribution functions (RDFs) and evaluate the
performance of some of the most popular partial atomic charge (PAC) methods for
obtaining these RDFs by molecular dynamics (MD) simulations. To this end, we
compare classical MD of a frozen solute in water and acetonitrile (ACN) with
quantum mechanics/molecular mechanics Born-Oppenheimer molecular dynamics
(QM/MM BOMD) simulations. The calculated RDFs show that the choice of a
suitable PAC method is dependent on the coordination number of the metal,
denticity of the ligands, and type of solvent. It is found that this selection
is less sensitive for water than ACN. Furthermore, a careful choice of the PAC
method should be considered for TMCs that exhibit a free direct coordination
site, such as . The results of this work show that
fast classical MD simulations with ChelpG/RESP or CM5 PACs can produce RDFs
close to those obtained by QM/MM MD and thus, provide reliable solvation
structures of TMCs to be used, e.g. in the analysis of scattering data
On the role of coherence in the transition from kinetics to dynamics: Theory and application to femtosecond unimolecular reactions
We consider the relation between observed pump–probe signals in the femtosecond regime and the kinetics of unimolecular reactions, that is, the exponential decay of reactants and the exponential rise of the product population, respectively. It is shown that the signals cannot be fully accounted for within standard approaches of unimolecular decay, conventionally used in the past, since interference effects between the quasi-bound vibrational states within the bandwidth of the pump laser cannot be neglected. When these effects are included, all features of the signals can be accounted for. We apply this theoretical treatment of coherent interference to examine the dynamics and kinetics of the quasi-bound transition configurations, and relate them to the decay rates of individual quasi-bound resonance states. The signals show multi-exponential behavior, reflecting the different decay rates of the resonance states, with an average rate constant (within the bandwidth of the pump laser) which can be extracted directly from the signals. The persistence of coherence is evident in the observed signals. The predissociation of NaI is used as a prototype for numerical illustration
On the role of coherence in the transition from kinetics to dynamics: Theory and application to femtosecond unimolecular reactions
We consider the relation between observed pump–probe signals in the femtosecond regime and the kinetics of unimolecular reactions, that is, the exponential decay of reactants and the exponential rise of the product population, respectively. It is shown that the signals cannot be fully accounted for within standard approaches of unimolecular decay, conventionally used in the past, since interference effects between the quasi-bound vibrational states within the bandwidth of the pump laser cannot be neglected. When these effects are included, all features of the signals can be accounted for. We apply this theoretical treatment of coherent interference to examine the dynamics and kinetics of the quasi-bound transition configurations, and relate them to the decay rates of individual quasi-bound resonance states. The signals show multi-exponential behavior, reflecting the different decay rates of the resonance states, with an average rate constant (within the bandwidth of the pump laser) which can be extracted directly from the signals. The persistence of coherence is evident in the observed signals. The predissociation of NaI is used as a prototype for numerical illustration
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