Semiclassical Molecular Dynamics for Spectroscopic Calculations

Abstract

We present some historical and recently developed techniques to perform semiclassical spectroscopy calculations with both ground and excited state dynamics. The illustrated topics begin with a derivation of the basic semiclassical van Vleck propagator starting from Feynman's path integral formulation, followed by the description of the initial value representation formalism and a derivation of the Heller-Herman-Kluk-Kay semiclassical propagator. The chapter continues by introducing the time averaging technique and its very recent developments consisting in the multiple coherent, divide-and-conquer, and mixed semiclassical approaches. The main features of each method are described through examples with the intent of helping readers have a gentle learning curve. The chapter ends with a workflow chart, a few representative applications, a summary, and some conclusions.

Qual È La Più Piccola Goccia D’acqua?

“…Nel mio gruppo di ricerca (https://sites.unimi.it/ceotto/) abbiamo recentemente sviluppato dei metodi basati sulla meccanica semiclassica [5][6][7][8][9][10][11][12][13], grazie ad un finanziamento dell'European Research Council. In particolare, abbiamo esteso le teorie semiclassiche al calcolo degli spettri vibrazionali di sistemi molecolari complessi e supramolecolari [14][15][16][17][18][19][20][21].…”

An effective semiclassical approach to IR spectroscopy

“…The multi-dimensional integral over the initial phase space conditions is usually performed by means of Monte Carlo techniques, and the method has been applied successfully in many instances, yielding accurate results. [58][59][60][61][62] However, the number of different classical trajectories to run is often prohibitively high for an effective interface to ab initio on-the-fly evaluations of energies and gradients.…”

Improved semiclassical dynamics through adiabatic switching trajectory sampling

“…For the calculations presented here we employed reference states |Ψ made of suitable combinations of coherent states centered at equilibrium coordinates and harmonically estimated momenta, in agreement with our previous works. [58] Finally, φ t ′ is the phase of the so-called Herman-Kluk prefactor…”