Dr. Nicole Helbig

ETSF Associated European Union

Nicole Helbig's picture
nehelbig [at] gmail [dot] com
++49 2461 613429
++49 2461 612850
Current position
Emmy-Noether Research Group Leader
Peter Grünberg Institut (PGI) and Institute for Advanced Simulation (IAS)
Forschungszentrum Jülich, Germany

Research Information

Research Overview

Reduced-density matrix functional theory

Strongly correlated systems, which are usually not very well described within DFT, can be treated rather accurately using the one-body reduced-density matrix as the basic variable. One main advantage compared to DFT is the knowledge of the kinetic energy as a functional of the one-body reduced-density matrix. Within reduced-density matrix functional theory (RDMFT) the chemical potential can be calculated from the derivative discontinuity of the exchange-correlation energy with respect to the particle number. The applications for closed- and open-shell systems show a very good agreement with experimental results and
state of the art CI calculations.

Exact properties of model systems

For the development and testing of any approximate method it is essential to investigate the behavior of exactly solvable model systems. These models can either be specific systems, for which the Schrödinger equation is solvable analytically, or systems of reduced dimensionality which can be solved with reasonable computational effort. I have recently investigated the dissociation of two-electron systems in one dimension and calculated the exact Kohn-Sham potential in these cases. As these systems become strongly correlated at large separation their exact Kohn-Sham potential is of specific interest due to the failure of standard DFT approximations in these cases. I am also investigating the exact one-body density matrix, and the corresponding natural orbitals and occupation numbers, for several model systems. From the results I expect to gain insight into the possibility to use the natural orbitals for the description of actual single-particle states, the time-evolution of the density matrix, and the validity of adiabatic approximations.

Related Research Areas

Latest publications

Real-space grids and the Octopus code as tools for the development of new simulation approaches for electronic systems
Xavier Andrade, David A. Strubbe, Umberto De Giovannini, Ask Hjorth Larsen, Micael J. T. Oliveira, Joseba Alberdi-Rodriguez, Alejandro Varas, Iris Theophilou, Nicole Helbig, Matthieu Verstraete, Lorenzo Stella, Fernando Nogueira, Alán Aspuru-Guzik, Alberto Castro, Miguel A. L. Marques, Ángel Rubio
Physical Chemistry Chemical Physics 17, 31371-31396 - 31396 (2015)
Orbitals from local RDMFT: Are they Kohn-Sham or natural orbitals?
Iris Theophilou, Nektarios N. Lathiotakis, Nikitas I. Gidopoulos, Angel Rubio, Nicole Helbig
Journal of Chemical Physics 143, 054106 (2015)