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ABSTRACT: We derive equations for nonadiabatic Ehrenfest molecular dynamics within the projector augmented-wave (PAW) formalism. The discretization of the electrons is time-dependent as the augmentation functions depend on the positions of the nuclei. We describe the implementation of the Ehrenfest molecular dynamics equations within the real-space PAW method. We demonstrate the applicability of our method by studying the vibration of NaCl, the torsional rotation of H(2)C=NH(2)(+) in both the adiabatic and the nonadiabatic regimes, and the hydrogen bombardment of C(40)H(16).
The Journal of chemical physics 04/2012; 136(14):144103. · 3.09 Impact Factor
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ABSTRACT: We present an all-electron method for time-dependent density functional theory which employs hierarchical nonuniform finite-element bases and the time-propagation approach. The method is capable of treating linear and nonlinear response of valence and core electrons to an external field. We also introduce (i) a preconditioner for the propagation equation, (ii) a stable way to implement absorbing boundary conditions, and (iii) a new kind of absorbing boundary condition inspired by perfectly matched layers.
The Journal of chemical physics 10/2011; 135(15):154104. · 3.09 Impact Factor
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ABSTRACT: We have derived equations for nonadiabatic Ehrenfest molecular dynamics which
conserve the total energy in the case of time-dependent discretization for
electrons. A discretization is time-dependent in all cases where it or part of
it depends on the positions of the nuclei, for example, in atomic orbital basis
sets, and in the projector augmented-wave (PAW) method, where the augmentation
functions depend on the nuclear positions. We have derived, implemented, and
analyzed the energy conserving equations and their most common approximations
for a 1D test system where we can achieve numerical results converged to a high
accuracy. Based on the observations in 1D, we implement and analyze the
Ehrenfest molecular dynamics in 3D using the PAW method and the time-dependent
density functional formalism. We demonstrate the applicability of our method by
carrying out calculations for small and medium sized molecules in both the
adiabatic and the nonadiabatic regime.
09/2011;
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ABSTRACT: We present for static density functional theory and time-dependent density functional theory calculations an all-electron method which employs high-order hierarchical finite-element bases. Our mesh generation scheme, in which structured atomic meshes are merged to an unstructured molecular mesh, allows a highly nonuniform discretization of the space. Thus it is possible to represent the core and valence states using the same discretization scheme, i.e., no pseudopotentials or similar treatments are required. The nonuniform discretization also allows the use of large simulation cells, and therefore avoids any boundary effects.
The Journal of chemical physics 09/2009; 131(5):054103. · 3.09 Impact Factor
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ABSTRACT: We present the implementation of the time-dependent density-functional theory both in linear-response and in time-propagation formalisms using the projector augmented-wave method in real-space grids. The two technically very different methods are compared in the linear-response regime where we found perfect agreement in the calculated photoabsorption spectra. We discuss the strengths and weaknesses of the two methods as well as their convergence properties. We demonstrate different applications of the methods by calculating excitation energies and excited state Born-Oppenheimer potential surfaces for a set of atoms and molecules with the linear-response method and by calculating nonlinear emission spectra using the time-propagation method.
The Journal of chemical physics 07/2008; 128(24):244101. · 3.09 Impact Factor
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ABSTRACT: We have studied quantum wires using the Green's function technique and the density-functional theory, calculating the electronic structure and the conductance. All the numerics are implemented using the finite-element method with a high-order polynomial basis. For short wires, i.e. quantum point contacts, the zero-bias conductance shows, as a function of the gate voltage and at a finite temperature, a plateau at around 0.7G_0. (G_0 = 2e^2/h is the quantum conductance). The behavior, which is caused in our mean-field model by spontaneous spin polarization in the constriction, is reminiscent of the so-called 0.7-anomaly observed in experiments. In our model the temperature and the wire length affect the conductance-gate voltage curves in the same way as in the measured data. Comment: 8 pages
06/2004;
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ABSTRACT: We use the effective-mass approximation and the density-functional theory with the local-density approximation for modeling two-dimensional nano-structures connected phase-coherently to two infinite leads. Using the non-equilibrium Green's function method the electron density and the current are calculated under a bias voltage. The problem of solving for the Green's functions numerically is formulated using the finite-element method (FEM). The Green's functions have non-reflecting open boundary conditions to take care of the infinite size of the system. We show how these boundary conditions are formulated in the FEM. The scheme is tested by calculating transmission probabilities for simple model potentials. The potential of the scheme is demonstrated by determining non-linear current-voltage behaviors of resonant tunneling structures. Comment: 13 pages,15 figures
08/2003;
