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This first-principles study investigates the interactions between amino acids and various types of montmorillonite clay surfaces, including a pristine surface, a surface with an oxygen vacancy, a surface with a silicon vacancy, and an Fe-doped surface. Our results show that all clay surfaces exhibit negative binding energies, indicating that the interaction between clay and amino acids is thermodynamically favorable. Among them, the surface with a Si vacancy displays the most negative binding energy, corresponding to the strongest interaction. We also examine the reactions between two alanine molecules to form a dipeptide molecule through the elimination of a water molecule in the absence of clay surfaces. The transition state search suggests that a proton transfer plays a critical role in the peptide bond formation based on structural and energetic features observed along the reaction path. Circular dichroism spectra computed for reactant, intermediate, and product states show distinct chiral signatures. Wave packet dynamics calculations indicate that quantum tunneling might be the mechanism underlying the reduced activation energy at low temperatures. These findings offer insight into the physicochemical processes at clay–amino acid interfaces and support the design of clay-based materials with applications in biotechnology and prebiotic chemistry. 

This study investigates the adsorption mechanism of CO3^(2−) on the (111) surface of tricalcium silicate (C3S) using density functional theory simulations. Two distinct adsorption configurations were identified: a tilted alignment with localised bonding to Ca ions and concentrated charge transfer, and a parallel orientation with delocalised interactions involving multiple Ca ions. Charge density analysis revealed charge transfer from the surface to the carbonate molecule, with electron accumulation around oxygen atoms of CO3^(2−). Partial density of states analysis showed significant changes near the Fermi level after adsorption, indicating the formation of new bonding states. Molecular dynamics simulations demonstrated that the tilted configuration stabilises the surface by reducing Ca ion mobility, while the parallel configuration leads to increased ion mobility and higher surface reactivity. These findings emphasise the importance of site-specific interactions and electronic structure changes in understanding CO2 mineralisation mechanisms in cementitious materials. 

Transition metal complexes are an ideal target system for the computational modeling of photoluminescence to further improve their applications as emitters. In addition to strongly absorbing visible light, their photoactivity is highly tunable due to a wide selection of ligands which can modify the nature of photoinduced charge transfer (CT) in the system. For photochemical purposes, a long-lived CT state is ideal. This is exemplified by ruthenium(II) tris(bipyridine), which achieves such a state by undergoing intersystem crossing (ISC) due to the large spin-orbit coupling (SOC) for the ruthenium metal center’s d-electrons.1 The mechanism by which the CT state’s long lifetime is achieved is through flipping the spin of the electron in the excited state, which makes for a spin-forbidden relaxation. Despite these strengths, ruthenium remains very cost-prohibitive due to its small natural abundance compared to other transition metals. For this reason, several analogs to copper(I) bis(phenanthroline) have been studied as systems that exhibit CT state lifetimes similar to those in ruthenium (II) tris(bipyridine).2 These analogs seek to improve the CT character of copper(I) bis(phenanthroline) by functionalization with electron withdrawing groups and by extending the ligands’ π-systems. This study employs density- functional theory (DFT) as a basis for the computation of photoinduced CT lifetimes and quantum yields by factoring in spin-polarization and SOC, while operating under the framework of Redfield theory.3 This treatment couples the system to a heat bath and moreover allows for the simulation of dynamics using a reduced density matrix. Redfield dynamics enables the simulation of CT state lifetimes with the inclusion of spin effects. Non-adiabatic couplings (NACs), calculated using an “on-the-fly” technique, are used to extract Redfield tensors which may then be used in the simulation of electronic relaxation over time. It is expected that both electron withdrawing groups and extensions to the ligands’ π-systems would increase the lifetime and quantum yield of photoluminescence. References: (1) (2) (3) Caspar, J. V.; Meyer, T. J. Photochemistry of Tris(2,2’-Bipyridine)Ruthenium(2+) Ion (Ru(Bpy)32+). Solvent Effects. J. Am. Chem. Soc. 1983, 105 (17), 5583–5590. https://doi.org/10.1021/ja00355a009. Lavie-Cambot, A.; Cantuel, M.; Leydet, Y.; Jonusauskas, G.; Bassani, D. M.; McClenaghan, N. D. Improving the Photophysical Properties of Copper(I) Bis(Phenanthroline) Complexes. Coordination Chemistry Reviews 2008, 252 (23–24), 2572–2584. https://doi.org/10.1016/j.ccr.2008.03.013. Redfield, A. G. The Theory of Relaxation Processes. In Advances in Magnetic and Optical Resonance; Elsevier, 1965; Vol. 1, pp 1–32. https://doi.org/10.1016/B978-1-4832-3114-3.50007-6. 

The efficiency of silicon solar cells is affected by the light absorption and recombination losses of photoexcited charge carries. One possible way to improve the efficiency is through the deposition of transition metal nanoparticles on Si surfaces. Here, we first carry out density functional theory (DFT) calculations to obtain electronic structures for Agn (n = 1–7) monolayered clusters adsorbed on Si(111)/H surfaces. Results are presented in the form of the density of states, band gaps, and light absorption, which allow for the investigation of the interaction of Ag clusters with Si. Different behaviors can be expected depending on the size of the deposited Ag clusters. Overall, the deposition of Ag clusters leads to smaller band gaps, red-shifts, and large increases in light absorption compared to the pristine Si slab. We then study the relaxation dynamics of electron–hole pairs for slabs based on nonadiabatic couplings using the reduced density matrix approach within the Redfield formalism. Nonradiative relaxation rates are noticeably different for various structures and transitions. One observes higher relaxation rates for surfaces with adsorbates than for the pristine Si surface due to charge transfer events involving Ag orbitals. We also compute emission spectra from excited-state relaxation dynamics. The band gap emission is dark for the pristine Si due to the indirect nature of its band gap. The addition of larger Ag clusters breaks the symmetry of Si slabs, enabling indirect gap transitions. These slabs thus exhibit bright band gap emission. The introduction of adsorbates is advantageous for applications in photovoltaics and photocatalysis. 

The optical properties of the tetragonal phase of BaTiO₃have been studied using density functional methods, applying the generalized gradient approximation at room temperature and a hybrid functional for static lattice analysis. 

Semiconducting conjugated polymers (CPs) are pivotal in advancing organic electronics, offering tunable properties for solar cells and field-effect transistors. Here, we carry out first-principle calculations to study individual cis-polyacetylene (cis-PA) oligomers and their ensembles. The ground electronic structures are obtained using density functional theory (DFT), and excited state dynamics are explored by computing nonadiabatic couplings (NACs) between electronic and nuclear degrees of freedom. We compute the nonradiative relaxation of charge carriers and photoluminescence (PL) using the Redfield theory. Our findings show that electrons relax faster than holes. The ensemble of oligomers shows faster relaxation compared to the single oligomer. The calculated PL spectra show features from both interband and intraband transitions. The ensemble shows broader line widths, redshift of transition energies, and lower intensities compared to the single oligomer. This comparative study suggests that the dispersion forces and orbital hybridizations between chains are the leading contributors to the variation in PL. It provides insights into the fundamental behaviors of CPs and the molecular-level understanding for the design of more efficient optoelectronic devices. 

The work provides computational arguments in support of excitonic approach for the treatment of the photo-induced processes in semiconductor quantum dots. The non-radiative relaxation, non-radiative recombination, and photo-luminescence quantum yield are computed for a range of atomistic models of semiconductor quantum dots (QDs) in the quantum confinement regime. The excitonic (EX) approach is compared to independent orbital approximation (IOA) approach. Both approaches address dissipation of the electronic energy from electronic degrees of freedom to thermal vibrations of the lattice. The difference of two approaches appears in treatment of energies of electronic states and in a way how the electron-phonon interaction is taken into account. IOA approach uses energies of Kohn-Sham orbitals and on the fly non-adiabatic couplings. [1-3] EX approach uses Bethe-Salpeter equation (BSE) for energies.[4-6] The excitonic wavefunctions from BSE is used to construct a linear transformation matrix that transforms IOA-based non-adiabatic couplings into an excitonic basis. Both approaches are compared in application to untrasmall 1 nm diameter Si QD.Results include an evidence that hot excitons relax sooner in the excitonic picture than in the IOA picture. The observed effect is rationalized via smaller subgaps and different available relaxation pathways in the excitonic picture. The most surprising result is found for the simulated emission spectrum. The spectum in the excitonic picture demonstrates intensity in several 5 orders of magnitude higher than in the IOA picture. This observation is related to formation of a bright exciton in the lowest excitation of the ultra-small Si QDs. Obtained evidence favors excitonic approach and promises a reliable interpretation and prediction of time-dependent observables in a range of semiconductor quantum dots of different composition, sizes, and surface environment.[7] Most intriguing results are expected for QDs representing interface between PbSe and CdSe. [8] Support of National Science foundation via NSF CHE-2004197 is gratefully acknowledged. [1] D. S. Kilin and D. A. Micha, “Relaxation of photoexcited electrons at a nanostructured Si(111) surface”, J. Phys. Chem. Lett. 1, 1073-1077 (2010). [2] D. J. Vogel and D. S. Kilin, "First-Principles Treatment of Photoluminescence in Semiconductors" J. Phys. Chem. C 119, 50, 27954–27964 (2015). [3] D. J. Vogel, A. B. Kryjevski, T. M. Inerbaev, and D. S. Kilin, "Photoinduced Single- and Multiple-Electron Dynamics Processes Enhanced by Quantum Confinement in Lead Halide Perovskite Quantum Dots", J. Phys. Chem. Lett. 8, 13, 3032–3039(2017). [4] A. B. Kryjevski and Dmitri Kilin, "Enhanced multiple exciton generation in amorphous silicon nanowires and films", Molec. Phys. 114, 365-379 (2016). [5] M. Rohlfing and S. G. Louie, "Electron-Hole Excitations in Semiconductors and Insulators", Phys. Rev. Lett. 81, 2312-2315 (1998). [6] T. Sander, G. Kresse, "Macroscopic dielectric function within time-dependent density functional theory—Real time evolution versus the Casida approach", J. Chem. Phys. 146, 064110 (2017). [7] S. V. Kilina, P. K. Tamukong, and D. S. Kilin, "Surface Chemistry of Semiconducting Quantum Dots: Theoretical Perspectives", Acc. Chem. Res. 49, 10, 2127–2135 (2016). [8] H. B. Griffin, A. B. Kryjevski, and Dmitri S. Kilin, "Ab initio calculations of through-space and through-bond charge-transfer properties of interacting Janus-like PbSe and CdSe quantum dot heterostructures", Molec. Phys., e2273415 (2023). 

Organic color centers (OCCs), generated by the covalent functionalization of single-walled carbon nanotubes, have been exploited for chemical sensing, bioimaging, and quantum technologies. However, monovalent OCCs can assume at least 6 different bonding configurations on the sp2 carbon lattice of a chiral nanotube, resulting in heterogeneous OCC photoluminescence emissions. Herein, we show that a heat-activated [2 + 2] cycloaddition reaction enables the synthesis of divalent OCCs with a reduced number of atomic bonding configurations. The chemistry occurs by simply mixing enophile molecules (e.g., methylmaleimide, maleic anhydride, and 4-cyclopentene-1,3-dione) with an ethylene glycol suspension of SWCNTs at elevated temperature (70–140 °C). Unlike monovalent OCC chemistries, we observe just three OCC emission peaks that can be assigned to the three possible bonding configurations of the divalent OCCs based on density functional theory calculations. Notably, these OCC photoluminescence peaks can be controlled by temperature to decrease the emission heterogeneity even further. This divalent chemistry provides a scalable way to synthesize OCCs with tightly controlled emissions for emerging applications. 

An exploration of the “on-the-fly” nonadiabatic couplings (NACs) for nonradiative relaxation and recombination of excited states in 2D Dion–Jacobson (DJ) lead halide perovskites (LHPs) is accelerated by a machine learning approach. Specifically, ab initio molecular dynamics (AIMD) of nanostructures composed of heavy elements is performed with the use of machine-learning force-fields (MLFFs), as implemented in the Vienna Ab initio Simulation Package (VASP). The force field parametrization is established using on-the-fly learning, which continuously builds a force field using AIMD data. At each time step of the molecular dynamics (MD) simulation, the total energy and forces are predicted based on the MLFF and if the Bayesian error estimate exceeds a threshold, an ab initio calculation is performed, which is used to construct a new force field. Model training of MLFF and evaluation were performed for a range of DJ-LHP models of different thicknesses and halide compositions. The MLFF-MD trajectories were evaluated against pure AIMD trajectories to assess the level of discrepancy and error accumulation. To examine the practical effectiveness of this approach, we have used the MLFF-based MD trajectories to compute NAC and excited-state dynamics. At each stage, results based on machine learning are compared to traditional ab initio based electronic dissipative dynamics. We find that MLFF-MD provides comparable results to AIMDs when MLFF is trained in an NPT ensemble.