Influence of Au, Ag, and Cu Adatoms on Optical Properties of TiO2 (110) Surface: Predictions from RT-TDDFT Calculations

Abstract

In this paper, real-time time-dependent density-functional theory (RT-TDDFT) calculations are performed to analyze the optical property and charge transitions of a single noble metal atom deposited on rutile TiO2 (110) surface. The model structures are built reflecting the equilibrium positions of deposited adatoms atop the TiO2 surface. The absorption spectra are calculated for all model structures under study. To provide deeper insight into photo-absorption processes, the transition contribution maps are computed for the states of deposited adatoms involved in transitions. Assuming the photon energy is enough to overcome the band gap of TiO2 (∼3 eV), the photogenerated electrons of TiO2 seem to be partly accumulated around deposited Au atoms. In contrast, this is rarely observed for deposited Ag and Cu atoms. Based on our calculations, we have identified the transition state mechanism that is important for the design strategy of future photocatalytic materials.

Excited State Calculations of Cu-Doped Anatase TiO2 (101) and (001) Nanofilms

“…However, a notable distinction for the TiO 2 (001) surface is that the enhancement in absorption is not confined to the x direction; it extends to the y and z directions as well. The observed slight red shift in the calculated absorption spectra aligns with our recent theoretical investigation involving Cu, Ag, and Au adatoms deposited onto the rutile TiO 2 (110) surface [23]. In cases where the noble metal adatom is not strongly bonded to the surface oxygen or other nearest host surface atoms, the calculated electronic structure of the pristine rutile TiO 2 (110) surface closely resembles that of the surface with an attached adatom.…”

“…When the Hubbard U parameter for titanium d-orbitals U Ti(d) = 4.2 eV is incorporated, the resulting optical absorption spectrum shows a red shift compared to neglect of the Hubbard correction. Interestingly, despite these adjustments, our analysis reveals that there is no significant difference in the absorption characteristics between the TiO 2 surfaces with and without the Hubbard correction [23,62,63]. This finding suggests that the Hubbard correction does not markedly alter the absorption properties of these surfaces, at least within the range of our study.…”

“…Despite the numerous merits of TiO 2 , its wide band gap (ranging from 3.0 to 3.2 eV [19]) limits efficient photoabsorption in the visible light region of the solar spectrum. To overcome this, integrating 3d metal dopants, such as copper [3,4,16,20], into TiO 2 has shown promise in boosting both its photocatalytic and antibacterial capabilities [21][22][23]. Copper introduces improvements by mitigating electron-hole pair recombination, thereby extending the lifespan of electrons and concurrently improving the photoresponse under visible light irradiation [18].…”

“…However, there are geometric configurations that are close to the minimum energy of equilibrium models and that still fulfill the criteria for convergence in DFT calculations. Although the absorption spectrum might display similarities across different geometries, variations in the electronic orbitals due to such different geometries could cause noticeable differences in the localization patterns of the transitions [23].…”

Density functional theory for doped TiO2: current research strategies and advancements

“…Summarizing this subsection, we observed that the majority of recent studies on doped TiO 2 have found the accuracy of optical property calculations conducted using several DFT-based computational techniques to be satisfactory. However, a few exceptions exist where more advanced techniques such as TDDFT, GW, or BSE methods were also employed [184,185]. These preferences indicate that despite its acknowledged limitations in describing optical properties, DFT still contributes to exploratory research.…”