352 citations · 3.4k across the 93 of their papers we have counts for
20 papers · 1 filter
Finite-size scaling of typicality-based estimates
J. Schnack, J. Richter, T. Heitmann +1
According to the concept of typicality, an ensemble average can be accurately approximated by an expectation value with respect to a single pure state drawn at random from a high-d…
Van Der Waals Revisited
K. Baerwinkel, J. Schnack
The van-der-Waals version of the second virial coefficient is not far from being exact if the model parameters are appropriately chosen. It is shown how the van-der-Waals resemblan…
Sampling the two-dimensional density of states g(E,M) of a giant magnetic molecule using the Wang-Landau method
S. Torbruegge, J. Schnack
The Wang-Landau method is used to study the magnetic properties of the giant paramagnetic molecule Mo_72Fe_30 in which 30 Fe3+ ions are coupled via antiferromagnetic exchange. The…
Quantum numbers for relative ground states of antiferromagnetic Heisenberg spin rings
K. Baerwinkel, P. Hage, H. -J. Schmidt +1
We suggest a general rule for the shift quantum numbers k of the relative ground states of antiferromagnetic Heisenberg spin rings. This rule generalizes well-known results of Mars…
Nose-Hoover sampling of quantum entangled distribution functions
D. Mentrup, J. Schnack
While thermostated time evolutions stand on firm grounds and are widely used in classical molecular dynamics (MD) simulations, similar methods for quantum MD schemes are still lack…
Improved upper and lower energy bounds for antiferromagnetic Heisenberg spin systems
K. Baerwinkel, H. -J. Schmidt, J. Schnack
Large spin systems as given by magnetic macromolecules or two-dimensional spin arrays rule out an exact diagonalization of the Hamiltonian. Nevertheless, it is possible to derive u…
Approximating parabolas as natural bounds of Heisenberg spectra: Reply on the comment of O. Waldmann
H. -J. Schmidt, J. Schnack, Marshall Luban
O. Waldmann has shown that some spin systems, which fulfill the condition of a weakly homogeneous coupling matrix, have a spectrum whose minimal or maximal energies are rather poor…
Heisenberg exchange parameters of molecular magnets from the high-temperature susceptibility expansion
H. -J. Schmidt, J. Schnack, Marshall Luban
We provide exact analytical expressions for the magnetic susceptibility function in the high temperature expansion for finite Heisenberg spin systems with an arbitrary coupling mat…
Partition functions and symmetric polynomials
H. -J. Schmidt, J. Schnack
We find a close correspondence between certain partition functions of ideal quantum gases and certain symmetric polynomials. Due to this correspondence it can be shown that a numbe…
Nose-Hoover dynamics for coherent states
D. Mentrup, J. Schnack
The popular method of Nose and Hoover to create canonically distributed positions and momenta in classical molecular dynamics simulations is generalized to a genuine quantum system…
Bounding and approximating parabolas for the spectrum of Heisenberg spin systems
H. -J. Schmidt, J. Schnack, Marshall Luban
We prove that for a wide class of quantum spin systems with isotropic Heisenberg coupling the energy eigenvalues which belong to a total spin quantum number S have upper and lower…
Molecular Dynamics for Fermions
H. Feldmeier, J. Schnack
The time-dependent variational principle for many-body trial states is used to discuss the relation between the approaches of different molecular dynamics models to describe indist…
Transition from quantum to classical Heisenberg trimers: Thermodynamics and time correlation functions
D. Mentrup, H. -J. Schmidt, J. Schnack +1
We focus on the transition from quantum to classical behavior in thermodynamic functions and time correlation functions of a system consisting of three identical quantum spins s th…
Ground state properties of antiferromagnetic Heisenberg spin rings
K. Baerwinkel, H. -J. Schmidt, J. Schnack
Exact ground state properties of antiferromagnetic Heisenberg spin rings with isotropic next neighbour interaction are presented for various numbers of spin sites and spin quantum…
Spin dynamics of quantum and classical Heisenberg dimers
D. Mentrup, J. Schnack, Marshall Luban
Analytical solutions for the time-dependent autocorrelation function of the classical and quantum mechanical spin dimer with arbitrary spin are presented and compared. For large sp…
Thermodynamic fermion-boson symmetry in harmonic oscillator potentials
H. -J. Schmidt, J. Schnack
A remarkable thermodynamic fermion-boson symmetry is found for the canonical ensemble of ideal quantum gases in harmonic oscillator potentials of odd dimensions. The bosonic partit…
Thermodynamics of the harmonic oscillator using coherent states
J. Schnack
The ongoing discussion whether thermodynamic properties can be extracted from a (possibly approximate) quantum mechanical time evolution using time averages is fed with an instruct…
Quasi-Particle Picture for Monatomic Gases
K. Baerwinkel, J. Schnack, U. Thelker
A quasi-particle theory for monatomic gases in equilibrium is formulated and evaluated to yield the exact virial contributions to the thermodynamic state functions in lowest order…
Investigations on finite ideal quantum gases
H. -J. Schmidt, J. Schnack
Recursion formulae of the N-particle partition function, the occupation numbers and its fluctuations are given using the single-particle partition function. Exact results are prese…
Molecular dynamics investigations on a quantum system in a thermostat
J. Schnack
The model quantum system of fermions in a one dimensional harmonic oscillator potential is investigated by a molecular dynamics method at constant temperature. Although in quantum…