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A multidomain decomposition method is presented for time-dependent density functional calculations. The multidomain decomposition approach divides the coordinate space into subdomains where local solutions are generated. The subdomain solutions are used as basis states to describe the time propagation of electronic wave functions in the whole system. The applicability and flexibility of the approach are demonstrated on various test systems including the calculation of the photoabsorption cross section of a graphene ribbon and a light-harvesting triad. [ABSTRACT FROM AUTHOR]

Using first-principles calculations, it is shown that the work function of graphene on copper can be adjusted by varying the concentration of intercalated alkali metals. Using density functional theory, we calculate the modulation of work function when Li, Na, or K are intercalated between graphene and a Cu(111) surface. The physical origins of the change in work function are explained in terms of phenomenological models accounting for the formation and depolarization of interfacial dipoles and the shift in the Fermi-level induced via charge transfer. [ABSTRACT FROM AUTHOR]

A method to calculate the transmission coefficient in multiterminal systems is presented. By adding a complex absorbing potential to the Hamiltonian of the semi-infinite leads, the problem of inverting an infinite dimensional matrix is transformed into a finite dimensional eigenvalue problem. Using this approach transmission coefficients are calculated for all energies at once. The accuracy of the approach is demonstrated with an analytically solvable model system. Numerical examples of a four-terminal graphene cross junction and six-terminal carbon nanotube junction are presented. [ABSTRACT FROM AUTHOR]

The spatial current distribution in H-terminated zigzag graphene nanoribbons (ZGNRs) under electrical bias is investigated using time-dependent density-functional theory solved on a real-space grid. A projected complex absorbing potential is used to minimize the effect of reflection at simulation cell boundary. The calculations show that the current flows mainly along the edge atoms in the hydrogen terminated pristine ZGNRs. When a vacancy is introduced to the ZGNRs, loop currents emerge at the ribbon edge due to electrons hopping between carbon atoms of the same sublattice. The loop currents hinder the flow of the edge current, explaining the poor electric conductance observed in recent experiments. [ABSTRACT FROM AUTHOR]

A real-space, real-time implementation of time-dependent density functional theory is used to study electron field emission from nanostructures. Carbon nanotubes and graphene nanoribbons are used as model systems. The calculations show that carbon nanotubes with iron adsorbates have spin-polarized emission currents. Graphene nanoribbons are shown to be good field emitters with spatial variation of the emission current influenced by the presence of passivating hydrogen. [ABSTRACT FROM AUTHOR]

The properties of carbon nanotube-graphene junctions are investigated with first-principles electronic structure and electron transport calculations. Contact properties are found to be key factors in determining the performance of nanotube based electronic devices. In a typical single-walled carbon nanotube-metal junction, there is a p-type Schottky barrier of up to ∼0.4 eV which depends on the nanotube diameter. Calculations of the Schottky barrier height in carbon nanotube-graphene contacts indicate that low barriers of 0.09 eV and 0.04 eV are present in nanotube-graphene contacts ((8,0) and (10,0) nanotubes, respectively). Junctions with a finite contact region are investigated with simulations of the current-voltage characteristics. The results suggest the suitability of the junctions for applications and provide insight to explain recent experimental findings. [ABSTRACT FROM AUTHOR]

The collision of energetic ions and graphene fragments is studied in the framework of real-space finite-difference time-dependent density functional theory (TDDFT) coupled with classical molecular dynamics for nuclei. The amount of energy transferred from the projectile to the target is calculated to explore the defect formation mechanisms as a function of the projectile's energy. It is found that creation of defects in graphene due to the interaction of a fast proton with valence electrons is unlikely. In the case of projectiles with higher charges, the transferred energy increases significantly, leading to higher probability of bond breaking. [ABSTRACT FROM AUTHOR]