Efficient canonical sampling
A Generalized Langevin dynamics can be tuned so that all the vibrational
modes in a system of interest behave as if critically damped. This results in a
more efficient sampling of the constant-temperature canonical ensemble.
Interestingly, this tuning can be done in a a-priori fashion, without knowledge
of the details of the system of interest, so that this optimal-sampling GLE
achieves near-ideal sampling efficiency without the need of optimizing the thermostat
parameters on the system of choice.
Quantum thermostat and PI+GLE
The quantum mechanical behavior of light nuclei (such as hydrogen) can have a dramatic effect
on physical properties of condensed phase systems. For instance, one can extrapolate the pH of
isotopically pure waters to the infinite-mass limit, and estimate that a 'classical' water
would have pH=8.5.
An appropriate GLE can enforce a phase-space distribution consistent with a quantum harmonic oscillator
without any significant overhead. This allows one to model nuclear quantum effects in a classical
simulation inexpensively. A systematic improvement of the accuracy in strongly anharmonic problems
can be achieved by combining this approach with path integral molecular dynamics
(with a much lower number of replicas than for a fully converged PI simulation).
PIGLET and particle momentum distribution
The PI+GLE method can be improved significantly by also enforcing the centroid fluctuations
to take on the converged value for a harmonic system and a small number of beads. This allows one
to compute the quantum kinetic energy estimator very efficiently, which in turns enables the calculation
of the amplitude of the particle momentum distribution.
By computing also the off-diagonal
terms of the kinetic energy tensor, and by performing appropriate running averages, one can also get
in an automatic fashion the anisotropy of the PMD, hence improving the comparison with DINS experiments
without resorting to open path integrals.
Selective normal mode excitation
By tuning the properties of the colored noise it is possible to realize a
stochastic dynamics in which only the normal modes within a narrow range of frquencies
are excited, without prior knowledge of the system's phonon spectrum.