# Simulating the Electronic Circular Dichroism of Chlorophyll b in the Presence of a Gold Nanosphere

## TL;DR

This paper studies how a gold nanoparticle affects the electronic circular dichroism of chlorophyll b using a multiscale simulation approach.

## Contribution

A real-time multiscale method is introduced to simulate plasmonic effects on the ECD of chlorophyll b near a gold nanosphere.

## Key findings

- Plasmonic effects significantly modify the ECD spectra of chlorophyll b depending on distance and orientation.
- An intense peak at 2.36 eV appears when chlorophyll b is oriented perpendicularly to the nanoparticle surface.
- The magnetic transition dipole moment increases by four to five times in specific orientations.

## Abstract

In this work, we apply a real-time multiscale approach
to investigate
plasmonic effects arising from a gold spherical nanoparticle (NP)
on the electronic circular dichroism (ECD) spectrum of Chlorophyll
b (Chlb). Chlb has been described within linear-response time-dependent
density functional theory (TDDFT) to obtain excitation energies and
transition dipole moments, which were then employed in a TD-CIS ansatz
for the time-dependent wave function, subsequently propagated by solving
the time-dependent Schrödinger equation. Three different distances
(1, 3, and 5 nm) of the molecule with respect to the surface of the
NP were considered. For each distance, three Chlb orientations (two
perpendicular and one parallel) were taken into account, together
with three pulse polarization directions. In addition, a simple descriptor
of the plasmon-induced signal enhancement or quenching of the signal
was introduced, based on the time-dependent coherences between the
electronic ground state and selected excited states. In general, modifications
in the ECD spectra of Chlb have been attributed to plasmonic effects.
An interesting exception is the appearance of an intense peak at 2.36
eV when Chlb is oriented perpendicularly to the NP surface and the
pulse is polarized perpendicular to the molecular plane. In this case,
the magnetic transition dipole moment to the second state (providing
the excitation at 2.36 eV) increases by a factor of four to five compared
to bare Chlb or other orientations. The composition of the excitations
was analyzed through the differential projected density of states.