Sökning: "density matrix methods"
Visar resultat 6 - 10 av 81 avhandlingar innehållade orden density matrix methods.
6. Numerical Methods for Molecular Dynamics with Nearly Crossing Potential Surfaces
Sammanfattning : This thesis consists of four papers that concern error estimates for the Born-Oppenheimer molecular dynamics, and adaptive algorithms for the Car-Parrinello and Ehrenfest molecular dynamics.In Paper I, we study error estimates for the Born-Oppenheimer molecular dynamics with nearly crossing potential surfaces. LÄS MER
7. Some Aspects of Non-Perturbative Quantum Field Theory
Sammanfattning : The aim of this thesis is to describe some different ways in which non-perturbative methods enter in quantum field theory. In the thesis such methods enter in 1+1-dimensional theories: various Yang-Mills theories and electrodynamics. It also enters when treating charged bosons or fermions interacting with an external, classical field. LÄS MER
8. Low-density parity-check codes : unequal error protection and reduction of clipping effects
Sammanfattning : The invention of low-density parity-check (LDPC) codes made reliable communication possible at transmission rates very close to the theoretical limit predicted by Shannon. However, communication close to the Shannon limit requires very long codes and results in long delay and high encoder and decoder complexity. LÄS MER
9. Fock Matrix Construction for Large Systems
Sammanfattning : This licentiate thesis deals with quantum chemistry methods for large systems. In particular, the thesis focuses on the efficient construction of the Coulomb and exchange matrices which are important parts of the Fock matrix in Hartree--Fock calculations. LÄS MER
10. Coarse Graining Monte Carlo Methods for Wireless Channels and Stochastic Differential Equations
Sammanfattning : This thesis consists of two papers considering different aspects of stochastic process modelling and the minimisation of computational cost. In the first paper, we analyse statistical signal properties and develop a Gaussian pro- cess model for scenarios with a moving receiver in a scattering environment, as in Clarke’s model, with the generalisation that noise is introduced through scatterers randomly flip- ping on and off as a function of time. LÄS MER