A quantum-mechanical Boltzmann equation for one-particle Γs-distribution functions

1978 ◽  
Vol 91 (1-2) ◽  
pp. 229-248 ◽  
Author(s):  
Eduard Prugovečki
1979 ◽  
Vol 34 (5) ◽  
pp. 585-593 ◽  
Author(s):  
M. Capitelli ◽  
M. Dilonardo

Abstract Electron energy distribution functions (EDF) of molecular H2 have been calculated by numerically solving the Boltzmann equation including all the inelastic processes with the addition of superelastic vibrational collisions and of the hydrogen atoms coming from the dissociation process. The population densities of the vibrational levels have been obtained both by assuming a Boltz-mann population at a vibrational temperature different from the translational one and by solving a system of vibrational master equations coupled to the Boltzmann equation. The results, which have been compared with those corresponding to a vibrationally cold molecular gas, show that the inclusion of superelastic collisions and of the parent atoms affects the EDF tails without strongly modifying the EDF bulk. As a consequence the quantities affected by the EDF bulk, such as average and characteristic energies, drift velocity, 0-1 vibrational excitation rate are not too much affected by the inclusion of superelastic vibrational collisions and of parent atoms, while a strong influence is observed on the dissociation and ionization rate coefficients which depend on the EDF tail. Calculated dissociation rates, obtained by EDF's which take into account both the presence of vibrationally excited molecules and hydrogen atoms, are in satisfactory agreement with experimental results.


2004 ◽  
Vol 76 (1) ◽  
pp. 37-47 ◽  
Author(s):  
C. F. Schwenk ◽  
B. M. Rode

The comparison of two different combined quantum mechanical (QM)/molecular mechanical (MM) simulations treating the quantum mechanical region at Hartree-Fock (HF) and B3-LYP density functional theory (DFT) level allowed us to determine structural and dynamical properties of the hydrated calcium ion. The structure is discussed in terms of radial distribution functions, coordination number distributions, and various angular distributions and the dynamical properties, as librations and vibrations, reorientational times and mean residence times were evaluated by means of velocity autocorrelation functions. The QM/MM molecular dynamics (MD) simulation results prove an eightfold-coordinated complex to be the dominant species, yielding average coordination numbers of 7.9 in the HF and 8.0 in the DFT case. Structural and dynamical results show higher rigidity of the hydrate complex using DFT. The high instability of calcium ion's hydration shell allows the observation of water-exchange processes between first and second hydration shell and shows that the mean lifetimes of water molecules in this first shell (<100 ps) have been strongly overestimated by conclusions from experimental data.


Author(s):  
Norman J. Morgenstern Horing

Chapter 6 introduces quantum-mechanical ensemble theory by proving the asymptotic equivalence of the quantum-mechanical, microcanonical ensemble average with the quantum grand canonical ensemble average for many-particle systems, based on the method of Darwin and Fowler. The procedures involved identify the grand partition function, entropy and other statistical thermodynamic variables, including the grand potential, Helmholtz free energy, thermodynamic potential, Gibbs free energy, Enthalpy and their relations in accordance with the fundamental laws of thermodynamics. Accompanying saddle-point integrations define temperature (inverse thermal energy) and chemical potential (Fermi energy). The concomitant emergence of quantum statistical mechanics and Bose–Einstein and Fermi–Dirac distribution functions are discussed in detail (including Bose condensation). The magnetic moment is derived from the Helmholtz free energy and is expressed in terms of a one-particle retarded Green’s function with an imaginary time argument related to inverse thermal energy. This is employed in a discussion of diamagnetism and the de Haas-van Alphen effect.


1967 ◽  
Vol 22 (12) ◽  
pp. 1871-1889 ◽  
Author(s):  
S. Hess

A generalized quantum mechanical Boltzmann equation is derived for the one particle distribution operator of a dilute gas consisting of molecules with arbitrary internal degrees of freedom. The effect of an external, time-independent potential on the scattering process is taken into account. The collision term of the transport equation contains the two-particle scattering operator T and its adjoint in a bilinear way and is non-local. The conservation equations for number of particles, energy, momentum and angular momentum as well as the H-theorem are deduced from the transport equation. One obtains the correct equilibrium distribution operator even in the presence of an external field (e. g. for particles with spin in a homogeneous magnetic field). Some special cases of the generalized Boltzmann equation are discussed treating position and momentum of a particle as classical variables but characterizing the internal state of a molecule by quantum mechanical observables. Using the local part of the collision term only and considering molecules with degenerate, but sufficiently separated internal energy levels one arrives at the Waldmann-Snider equation, which in turn comprises the Waldmann equation for particles with spin and the Wang Chang-Uhlenbeck equation. Special attention is drawn to the case of particles with spin in a magnetic field. Finally, for particles with spin, the local conservation equation for angular momentum, i.e. the Barnett effect (magnetization by rotation) and the antisymmetric part of the pressure tensor are derived from the generalized Boltzmann equation with non-local collision term.


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