Torsional autocorrelation function

The divergence between the rate of conformational transitions and the decay of the torsional autocorrelation functions (and hence local relaxations)... 

The effect of introducing norbomene-substituted, pendant POSS moieties onto polynorbomene chains was explored by BharadwaJ et al. using atomistic molecular dynamics simulations (AMDS). The mobUity of the POSS moieties in these copolymers was addressed via the mean squared displacement of the POSS polyhydra in flie norbomene copolymers of 16a and Idb. Computation of the torsional autocorrelation function indicated ttiat conformational dynamics were retarded by the presence of the POSS moieties. The main chain dynamics were sensitive to the presence and tile nature of the attached POSS moieties (at 10 mol % POSS). Chain dynamics were slower in the copolymer with cyclohexyl-substituted POSS pendent groups compared to the copolymer with cyclopentyl-substituted POSS pendant groups. These results are in good agreement with the mechanical properties predicted from AMDS simulations and with the observed Tg values. The simulations predicted... 

In an ambitious study, the AIMS method was used to calculate the absorption and resonance Raman spectra of ethylene [221]. In this, sets starting with 10 functions were calculated. To cope with the huge resources required for these calculations the code was parallelized. The spectra, obtained from the autocorrelation function, compare well with the experimental ones. It was also found that the non-adiabatic processes described above do not influence the spectra, as their profiles are formed in the time before the packet reaches the intersection, that is, the observed dynamic is dominated by the torsional motion. Calculations using the Condon approximation were also compared to calculations implicitly including the transition dipole, and little difference was seen. 

Figure 5 State autocorrelations computed from 100 ns butane simulations. The central torsion was labeled as either trans, g+, or g—, and the autocorrelation function for presence in each state was computed.

Figure 3. Temperature dependence of several meEtsures of the local orientational mobility of the chain. The lower set of curves pertaining to the right abscissa shows the mean time between torsional transitions for the three relevant torsional angles along the chain. The upper two sets of curves give the integrated autocorrelation time for the second Legendre polynomial of the CH vector orientation, rcH, and the integrated autocorrelation time for the torsion angle autocorrelation function, rroa-...

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