Recent advances in Frozen-Density Embedding: State-Selective Excitations, Charge Transfer, Spin Densities

ADF developer Johannes Neugebauer and his co-workers have showcased new methodologies within the Frozen-Density Embedding (FDE) framework. With FDE, much larger systems can be studied than with traditional DFT. Furthermore, as densities can be localized in fragments in a natural fashion in FDE, some well-known problem such as charge and spin delocalization can be overcome.

FDE has been complemented with state-selective excitations, facilitating the computation of excited state potential energy surfaces for large systems, e.g. to study surface-enhanced Raman scattering of molecules on nano-particles.
Electronic couplings are calculated by generating charge-localized, diabatic states directly with FDE, so that electron or hole transfer reactions between large fragments such as DNA strands can be studied.
The open-shell generalization of FDE to overcomes the overdelocalization of spin plaguing traditional DFT and even SIC-DFT. The spin-density asymmetry of a special pair radical cation model (750 atoms) has been scrutinized.

Recent methodological advances in Frozen-Density Embedding. Top left: FDE can be combined with state-selection to map out excited state PESs. Top right: Diabatic states to study charge transfer between fragments. Bottom: Spin-densities are localized correctly with open-shell FDE, not with SIC-DFT.

Another recent application by König and Neugebauer of FDE-TDDFT is on the First-Principles Calculation of Electronic Spectra of Light-Harvesting Complex II, a system consisting of 1100 atoms!

FDE, FDE-TDDFT, excited state PESs

A. Kovyrshin and J. Neugebauer Potential-energy surfaces of local excited states from subsystem- and selective Kohn-Sham-TDDFT. Chem. Phys., 391, 147-156 (2011).
M. Pavanello and J. Neugebauer Modelling charge transfer reactions with the frozen density embedding formalism. J. Chem. Phys., 135, 234103 (2011).
A. Solovyeva, M. Pavanello, and J. Neugebauer Spin densities from subsystem density-functional theory: Assessment and application to a photosynthetic reaction center complex model J. Chem. Phys., 136, 194014 (2012).
C. König and J. Neugebauer First-Principles Calculation of Electronic Spectra of Light-Harvesting Complex II. Phys. Chem. Chem. Phys., 13, 10475-10490 (2011).

Key concepts