We performed ab initio numerical simulations with the density functional theory to investigate the variations in the band structure, optical absorption, and the reflectivity of vacancy-graphene doped with nitrogen, oxygen, and fluorine for different densities. We considered the density values 0.78%, 1.02%, 1.39%, 2.00%, 3.12%, 5.55%, and 12.5% for the vacancies and doping. In the infrared and visible ranges for all cases, vacancies included, there is a substantial increment in the absorption and reflectivity concerning graphene. The most significant changes are for fluorine and oxygen at a concentration of 12.5%.

We investigated the effect of doping a hexagonal boron nitride surface (hBN) with Ti or Pt on the adsorption of CO₂. We performed first-principles molecular dynamics simulations (FPMD) at atmospheric pressure, and 300 K. Pristine hBN shows no interaction with the CO₂ molecule. We allowed the Ti and Pt atoms to interact separately, with either a B-vacancy or an N-vacancy. Both Ti and Pt ended chemisorbed on the surface. The system hBN + Ti always chemisorbed the CO₂ molecule. This chemisorption happens in two possible ways. One is without dissociation, and in the other, the molecule breaks in CO and O. However, in the case of the Pt atom as dopant, the resulting system repels the CO₂ molecule.

We investigated the possible adsorption of each of the main building blocks of spider silk: alanine, glycine, leucine, and proline. This knowledge could help develop new biocompatible materials and favors the creation of new biosensors. We used ab initio density functional theory methods to study the variations in the optical absorption, reflectivity, and band structure of a modified graphene surface interacting with these four molecules. Four modification cases were considered: graphene with vacancies at 5.55% and fluorine, nitrogen, or oxygen doping, also at 5.55%. We found that, among the cases considered, graphene with vacancies is the best candidate to develop optical biosensors to detect C=O amide and differentiate glycine and leucine from alanine and proline in the visible spectrum region. Finally, from the projected density of states, the main changes occur at deep energies. Thus, all modified graphene’s electronic energy band structure undergoes only tiny changes when interacting with amino acids.

We performed ab initio DFT calculations to explore the optical properties of a hexagonal boron nitride (hBN) monolayer, doped with a Ti or a Pt atom. Ti doping increases the adsorption capability of the boron nitride surface for capturing CO₂. Both doping types increase the optical absorption and reflectivity of the hBN surface in the infrared and visible regions. For the UV region, a B vacancy increases the absorption of the hBN sheet. Captured CO₂ bears substantial changes in the optical absorption and reflectivity spectra of the system considered.

Using structural relaxation calculations and first-principles molecular dynamics (FPMD), we performed numerical simulations to explore the interaction of a 2D MoS₂ surface and a platinum atom, calculating the optical properties of the resulting material. We explored three initial positions for the interaction of the Pt atom and the pristine MoS₂ surface, plus another position between Pt and the MoS₂ surface with a sulfur vacancy V_S. The surface absorbed the Pt atom in all cases considered, with absorption energies ranging from −2.77 eV to −5.83 eV. We calculated the optical properties and band structure of the two cases with the largest absorption energies (−3.45 eV and −5.83 eV). The pristine MoS₂ is a semiconductor with a gap of around 1.80 eV. With the adsorption of the Pt atom (the −3.45 eV case), the material reduces its band gap to 0.95 eV. Additionally, the optical absorption in the visible range is greatly increased. The energy band structure of the 2D MoS₂ with a sulfur vacancy V_S shows a band gap of 0.74 eV, with consequent changes in its optical properties. After the adsorption of Pt atoms in the V_S vacancy, the material has a band gap of 1.06 eV. In this case, the optical absorption in the visible range increases by about eight times. The reflectivity in the infrared range gets roughly doubled for both situations of the Pt-absorbed atom considered. Finally, we performed two FPMD runs at 300 K to test the stability of the cases with the lowest and highest absorption energies observed, confirming the qualitative results obtained with the structural relaxations.

Understanding the interactions between molecules and sensing elements is crucial to improving sensors. We present one step toward getting closer to the breach between theory and empirical sensor development. Through density functional theory (DFT) calculations, we explored the changes in some optical properties of pristine graphene (G), graphene oxide (GO), and reduced graphene oxide (rGO) interacting with one molecule of acetaminophen (APAP). The main goal is to unveil which graphene-G, GO, and rGO-works better as a substrate to detect APAP for sensor applications based on UV/vis and near-infrared absorption, refractive index changes, and plasmon resonances. For this effort, we used Quantum ESPRESSO software. We calculated each supercell's adsorption energy and recovery time containing the APAP and one graphene variant. Afterward, we calculated the optical absorption, refractive index, reflectivity, and electron energy loss spectroscopy (EELS), a technique to identify the material's plasmons. Then, we analyzed the changeovers in the optical properties mentioned for each graphene layer with and without APAP. We found that G works for UV/vis and plasmon sensors operating in blue and UV-C regions; GO has the highest performance range in UV/vis and plasmonic sensors operating in UV-C; rGO has the highest performance range in UV/vis sensors working on near-infrared and UV-C. Additionally, rGO plasmonic sensors present an "oscillation of percentage variations" from visible to UV. Our study offers a strategy for creating a map to select the best substrate to develop selective APAP optical sensors.