Current research

Currently, I am working on a project on the interlayer binding in graphite, using ab initio quantum Monte Carlo methods implemented in the CASINO code. The weak binding is dominated by London dispersion forces which are not reproduced at all by commonly used density functional methods based on local or semilocal approximations. Most dispersion corrections that are based on atomistic models still fail to capture the the very special semi-metallic electronic structure of the graphene sheets. Diffusion Monte Carlo, on the other hand, naturally includes the long ranged correlations directly within the ab initio quantum system. The remaining challenge is the extreme precision necessary to describe the small energy differences in combination with a system size that drives the method to the limits of what is currently computationally possible.

General research interests

• Computational quantum physics
• Solid state theory
• Programming languages and tools for scientific computing and software design

Scientific expertise

• Electronic structure and transport properties
  ⇒ contacts, disorder, magnetic fields, spin transport
• Nanostructures
  ⇒ carbon nanotubes, graphene, graphite
• Monte-Carlo simulations
  ⇒ Quantum Monte Carlo (CASINO), lattice gauge theory, quantum field theory
• Density functional theory
  ⇒ SIESTA, ADF, CASTEP, Crystal

Publications

Diffusion Monte Carlo: Exponential scaling of computational cost for large systems

N. Nemec, Phys. Rev. B 81, 035119 (2010)

doi:10.1103/PhysRevB.81.035119 arXiv:0906.0501

Benchmark all-electron ab initio quantum Monte Carlo calculations for small molecules

N. Nemec, M. D. Towler, and R. J. Needs, J. Chem. Phys. 132, 034111 (2010)

doi:10.1063/1.3288054 arXiv:0908.2041

Modeling extended contacts to nanotube and graphene devices

N. Nemec, D. Tománek and G. Cuniberti, Phys. Rev. B 77, 125420 (2008)

doi:10.1103/PhysRevB.77.125420 arXiv:0711.1088

Quantum Transport in Carbon-based Nanostructures

N. Nemec, PhD-thesis, Universität Regensburg (July 2007)

URL: http://www.opus-bayern.de/uni-regensburg/volltexte/2007/848/

Hofstadter Butterflies of Bilayer Graphene

N. Nemec and G. Cuniberti, Phys. Rev. B 75, 201404(R) (2007)

doi:10.1103/PhysRevB.75.201404 arXiv:cond-mat/0612369

Hofstadter Butterflies of Carbon Nanotubes: Pseudofractality in the magnetoelectronic spectrum

N. Nemec and G. Cuniberti, Phys. Rev. B 74, 165411 (2006)

doi:10.1103/PhysRevB.74.165411 arXiv:cond-mat/0607096

Contact dependence of carrier injection in carbon nanotubes: An ab initio study

N. Nemec, D. Tománek and G. Cuniberti, Phys. Rev. Lett. 96, 076802 (2006)

doi:10.1103/PhysRevLett.96.076802 arXiv:cond-mat/0512396

Spin transport in disordered single-wall carbon nanotubes contacted to ferromagnetic leads

S. Krompiewski, N. Nemec and G. Cuniberti, Phys. Status Solidi (B) 243, 179 (2006)

doi:10.1002/pssb.200562410 arXiv:cond-mat/0509148