Frozen-Density Embedding Theory based simulations with experimental electron densities

• Published in: arXiv.org 2020-06
• Main Authors: Ricardi, Niccolò, Ernst, Michelle, Macchi, Piero, Wesolowski, Tomasz A
• Format: Article
• Language: English
• Subjects: Chromophores; Density; Embedding; Hydrogen bonding; Independent variables; Simulation
• ISSN: 2331-8422

The basic idea of Frozen-Density Embedding Theory (FDET) is the constrained minimisation of the Hohenberg-Kohn density functional \(E^{HK}[\rho]\) performed using the auxiliary functional \(E_{v_{AB}}^{FDET}[\Psi_A,\rho_B]\), where \(\Psi_A\) is the embedded \(N_A\)-electron wave-function and \(\rho_B(\vec{\mathrm{r}})\) a non-negative function in real space integrating to a given number of electrons \(N_B\). This choice of independent variables in the total energy functional \(E_{v_{AB}}^{FDET}[\Psi_A,\rho_B]\) makes it possible to treat the corresponding two components of the total density using different methods in multi-level simulations. We demonstrate, for the first time, the applications of FDET using \(\rho_B(\vec{\mathrm{r}})\) reconstructed from X-ray diffraction data on a molecular crystal. For eight hydrogen-bonded clusters involving a chromophore (represented with \(\Psi_A\)) and the glycylglycine molecule (represented as \(\rho_B(\vec{\mathrm{r}})\)), FDET is used to derive excitation energies. It is shown that experimental densities are suitable to be used as \(\rho_B(\vec{\mathrm{r}})\) in FDET based simulations.