Andreas Dullweber | University of Cambridge (original) (raw)

Papers by Andreas Dullweber

Research paper thumbnail of Split-Hamiltonian methods for rigid body molecular dynamics

Research paper thumbnail of Simple Quantum Mechanical Phenomena and the Feynman Real Time Path Integral

The path integral formalism gives a very illustrative and intuitive understanding of quantum mech... more The path integral formalism gives a very illustrative and intuitive understanding of quantum mechanics but due to its difficult sum over phases one usually prefers Schr\"odinger's approach. We will show that it is possible to calculate simple quantum phenomena by performing Feynman's sum over all paths staying entirely in real time. Once the propagator is obtained it is particularly easy to get the energy spectrum or the evolution of any wavefunction.

Research paper thumbnail of ORIENT version 4.6

ORIENT is a program for carrying out calculations of various kinds for an assembly of interacting... more ORIENT is a program for carrying out calculations of various kinds for an assembly of interacting molecules. It uses a site-site potential specified by the user, including electrostatic, induction, repulsion, dispersion and charge-transfer interactions if required. ...

Research paper thumbnail of ORIENT version 4.6

Research paper thumbnail of Infrared spectra of argon clusters

Molecular Physics, 1998

We calculate far infrared absorption spectra and permanent dipole moments for neutral argon clust... more We calculate far infrared absorption spectra and permanent dipole moments for neutral argon clusters with up to 110 atoms. The model includes many-body dispersion, exchange quadrupoles and induction effects following the scheme proposed by Hutson and co-workers. The exchange quadrupoles are represented by dipoles pointing away from each other along the interatomic axes. We present predictions for future experiments and

Research paper thumbnail of Symplectic splitting methods for rigid body molecular dynamics

The Journal of Chemical Physics, 1997

Rigid body molecular models possess symplectic structure and time-reversal symmetry. Standard num... more Rigid body molecular models possess symplectic structure and time-reversal symmetry. Standard numerical integration methods destroy both properties, introducing nonphysical dynamical behavior such as numerically induced dissipative states and drift in the energy during long term simulations. This article describes the construction, implementation, and practical application of fast explicit symplectic-reversible integrators for multiple rigid body molecular simulations. These methods use a

Research paper thumbnail of Structure, dynamics, and thermodynamics of benzene-Arn clusters (1≤n≤8 and n=19)

The Journal of Chemical Physics, 1997

We use a combination of molecular dynamics, Monte Carlo and geometry optimisation techniques to s... more We use a combination of molecular dynamics, Monte Carlo and geometry optimisation techniques to study benzene-Ar n clusters for 1рnр19, with particular emphasis on BzAr 19 . In particular, we discuss the difficulties which arise in the accurate simulation of heterogeneous clusters due to problems of ergodicity and nonadditive contributions to the energy. The sensitivity of minima, transition states and reaction pathways to parameters of the potential and the induction energy is also considered. An efficient integration scheme with adaptive step size due to Bulirsch and Stoer is employed in the molecular dynamics simulations. Both geometry optimisation and molecular dynamics are considered to evaluate the usefulness of the Jump-walking Monte Carlo method proposed by Frantz, Freeman, and Doll. This approach improves the ergodicity of canonical simulations using data from different temperatures which we achieved using multiple parallel runs. We then apply a multiple histogram method to calculate the relative number of states in phase space and various thermodynamic properties covering the full temperature range in the canonical and the microcanonical ensembles. The Monte Carlo and molecular dynamics simulations result in a consistent picture of transitions between minima and escape times. Finally, we consider the rate of side-crossing by Ar atoms in BzAr 1 and BzAr 19 and compare statistical theories with rates obtained from simulations.

Research paper thumbnail of Structural predictions for (C60)N clusters with an all-atom potential

Chemical Physics Letters, 1997

We calculate the structures of neutral (C60)N clusters up to N = 56 using an all-atom potential t... more We calculate the structures of neutral (C60)N clusters up to N = 56 using an all-atom potential to test our prediction that face-centred-cubic geometries are favourable at small sizes due to the short range of the intermolecular potential. We find that above N = 17 the lowest energy structures are either decahedral or face-centred-cubic rather than icosahedral and discuss how

Research paper thumbnail of Split-Hamiltonian methods for rigid body molecular dynamics

Research paper thumbnail of Simple Quantum Mechanical Phenomena and the Feynman Real Time Path Integral

The path integral formalism gives a very illustrative and intuitive understanding of quantum mech... more The path integral formalism gives a very illustrative and intuitive understanding of quantum mechanics but due to its difficult sum over phases one usually prefers Schr\"odinger's approach. We will show that it is possible to calculate simple quantum phenomena by performing Feynman's sum over all paths staying entirely in real time. Once the propagator is obtained it is particularly easy to get the energy spectrum or the evolution of any wavefunction.

Research paper thumbnail of ORIENT version 4.6

ORIENT is a program for carrying out calculations of various kinds for an assembly of interacting... more ORIENT is a program for carrying out calculations of various kinds for an assembly of interacting molecules. It uses a site-site potential specified by the user, including electrostatic, induction, repulsion, dispersion and charge-transfer interactions if required. ...

Research paper thumbnail of ORIENT version 4.6

Research paper thumbnail of Infrared spectra of argon clusters

Molecular Physics, 1998

We calculate far infrared absorption spectra and permanent dipole moments for neutral argon clust... more We calculate far infrared absorption spectra and permanent dipole moments for neutral argon clusters with up to 110 atoms. The model includes many-body dispersion, exchange quadrupoles and induction effects following the scheme proposed by Hutson and co-workers. The exchange quadrupoles are represented by dipoles pointing away from each other along the interatomic axes. We present predictions for future experiments and

Research paper thumbnail of Symplectic splitting methods for rigid body molecular dynamics

The Journal of Chemical Physics, 1997

Rigid body molecular models possess symplectic structure and time-reversal symmetry. Standard num... more Rigid body molecular models possess symplectic structure and time-reversal symmetry. Standard numerical integration methods destroy both properties, introducing nonphysical dynamical behavior such as numerically induced dissipative states and drift in the energy during long term simulations. This article describes the construction, implementation, and practical application of fast explicit symplectic-reversible integrators for multiple rigid body molecular simulations. These methods use a

Research paper thumbnail of Structure, dynamics, and thermodynamics of benzene-Arn clusters (1≤n≤8 and n=19)

The Journal of Chemical Physics, 1997

We use a combination of molecular dynamics, Monte Carlo and geometry optimisation techniques to s... more We use a combination of molecular dynamics, Monte Carlo and geometry optimisation techniques to study benzene-Ar n clusters for 1рnр19, with particular emphasis on BzAr 19 . In particular, we discuss the difficulties which arise in the accurate simulation of heterogeneous clusters due to problems of ergodicity and nonadditive contributions to the energy. The sensitivity of minima, transition states and reaction pathways to parameters of the potential and the induction energy is also considered. An efficient integration scheme with adaptive step size due to Bulirsch and Stoer is employed in the molecular dynamics simulations. Both geometry optimisation and molecular dynamics are considered to evaluate the usefulness of the Jump-walking Monte Carlo method proposed by Frantz, Freeman, and Doll. This approach improves the ergodicity of canonical simulations using data from different temperatures which we achieved using multiple parallel runs. We then apply a multiple histogram method to calculate the relative number of states in phase space and various thermodynamic properties covering the full temperature range in the canonical and the microcanonical ensembles. The Monte Carlo and molecular dynamics simulations result in a consistent picture of transitions between minima and escape times. Finally, we consider the rate of side-crossing by Ar atoms in BzAr 1 and BzAr 19 and compare statistical theories with rates obtained from simulations.

Research paper thumbnail of Structural predictions for (C60)N clusters with an all-atom potential

Chemical Physics Letters, 1997

We calculate the structures of neutral (C60)N clusters up to N = 56 using an all-atom potential t... more We calculate the structures of neutral (C60)N clusters up to N = 56 using an all-atom potential to test our prediction that face-centred-cubic geometries are favourable at small sizes due to the short range of the intermolecular potential. We find that above N = 17 the lowest energy structures are either decahedral or face-centred-cubic rather than icosahedral and discuss how