Size-Dependence of the Enhanced Raman Scattering of Pyridine Adsorbed on Ag_n (n = 2−8, 20) Clusters

Abstract

We present a time-dependent density functional theory (TDDFT) study of the size-dependence of the absorption and Raman scattering properties of pyridine interacting with small silver nanoclusters Ag n (n ) 2-8, 20). By employing a recently developed short-time approximation for the Raman scattering cross section we simulate both the normal and the "surface"-enhanced Raman spectra. The absorption spectra of the small silver clusters are studied both in the gas phase and embedded in rare gas matrices. We find that both the absorption and Raman properties depend strongly on cluster size and adsorption site. The normal Raman spectra of Ag npyridine complexes resemble that of isolated pyridine, with enhancements which increase as cluster size increases. In contrast to this, both the enhancement and the appearance of the "surface"-enhanced Raman spectrum show a very strong dependence on cluster size. The total enhancements for the complexes are between 10 3 and 10 4 and quite surprisingly the strongest enhancement is found for the Ag 2 -Py complex. However, the enhancement trends can be correlated with the distance of the molecule to the center of the metal cluster and with the resonance polarizability in a way that is suggestive of electromagnetic enhancements, so the enhancement mechanism for these small clusters is similar to what is found for larger particles.

Time-dependent current-density functional theory for generalized open quantum systems

“…Ultimately, our goal is to apply this formulation to a realistic system where the non-Hamiltonian evolution is essential to understand its function, such as excitation transfer in chromophores embedded in a protein environment 10 or resonant surface enhanced Raman scattering. 4 In summary, our work provides an alternative tool to study generalized open quantum systems within the realm of TD-CDFT. instance, hnˆ(r )i t is the expectation value of the particle density operator at time t. Although this may appear redundant for explicitly time dependent operators, such as the current density, where we write hĵðr; tÞi t instead of just hĵðr; tÞi, we shall keep the notation throughout the article for consistency and clarity.…”

“…As an example, environmental effects are central in quantum decoherence and quantum thermodynamics, and the framework to study them is open quantum systems (OQS). 1,2 With the increasing possibility of designing, manipulating and controlling objects at the nanoscale, manybody OQS are becoming ubiquitous subjects of study in current research spanning a broad range of disciplines in the physical sciences from traditional condensed matter 3 and chemical physics, 4 to the emerging fields of biophysics 5 and quantum information science. 6 In order to achieve a substantial understanding of these systems, accurate yet computationally tractable theoretical techniques to study their time evolution are required.…”

Metal−Molecule Schottky Junction Effects in Surface Enhanced Raman Scattering

“…The Becke-Perdew (BP86) XC-potential [91,92] and a triple-polarized slater type (TZP) basis set from the ADF basis set library were used in our simulation. The validity of using DFT and ADF for quantum mechanical SERS calculation has already been proven by many researchers [37][38][39][40][41][42][43][44][45][46][47][48].…”

Tunability of the optical absorption in small silver cluster-polymer hybrid systems

“…They observed a strong size-and structural-dependence of the photoabsorption and photofragmentation in these systems. Other examples of recent TDDFT work on silver-cluster-organiccompound hybrid structures include a study of the enhancement mechanism in surface enhanced Raman scattering [36][37][38] and the determination of the optical properties of silver-cluster-biomolecule-hybrids. 39 In this paper, we study the effect of organic compounds on the photoabsorption spectra of silver cluster systems.…”