Equilibrium Geometric Structures Research Articles

Dual-Emission Origins in Bi3+-Doped M2O3 Sesquioxides (M = Sc, Y, Gd and Lu): A First-Principles Study.

Bi3+-doped sesquioxides exhibit dual emissions, marked by distinct Stokes shift and bandwidth, meaning unraveling their underlying origins is particularly intriguing. In this study, we employ first-principles calculations to investigate the luminescence mechanisms within the M2O3:Bi3+ (M = Sc, Y, Gd, Lu) series, with the goal of addressing the posed inquiry. Our investigation commences with the analysis of the site occupancy and charge state of bismuth ions in the two cationic sites through formation energy calculations. Additionally, we examine the local coordination environments for various excited states of Bi3+ dopants, including the 3P0,1 state and two types of charge transfer states, by evaluating their equilibrium geometric structures. The utilization of the hybrid functional enables us to obtain results of electronic structures and optical properties comparable with experiments. Importantly, the calculated energies for the 6s-6p transitions of Bi3+ dopants in the M2O3 series align well with the observed dual-emission energies. This alignment challenges the conventional spectroscopic sense that emission bands with large Stokes shifts can be exclusively ascribed to charge transfer transitions. Consequently, the integration of experimental and theoretical approaches emerges as the optimal strategy for designing novel Bi3+-doped phosphors.

Designed complexes combining brazilein and brazilin with betanidin for dye-sensitized solar cell application: DFT and TD-DFT study

Dye-sensitized solar cells (DSSCs) are promising third-generation photovoltaic cell technology owing to their easy fabrication, flexibility and better performance under diffuse light conditions. Natural pigment sensitizers are abundantly available and environmentally friendliness. However, narrow absorption spectra of natural pigments result in low efficiencies of the DSSCs. Therefore, combining two or more pigments with complementary absorption spectra is considered an appropriate method to broaden the absorption band and boost efficiency. This study reports three complex molecules: brazilin-betanidin-oxane (Braz-Bd-oxane), brazilin-betanidin-ether (Braz-Bd-ether) and brazilein-betanidin-ether (Braze-Bd-ether), obtained from the etherification and bi-etherification reactions of brazilin dye and brazilein dye with betanidin dye. The equilibrium geometrical structure properties, frontier molecular orbital, electrostatic surface potential, reorganization energy, chemical reactivities, and non-linear optical properties of the studied dyes were investigated using density functional theory (DFT)/B3LYP methods, with 6-31+G(d,p) basis sets and LANL2DZ for light atom and heavy atoms respectively. The optical-electronic properties were calculated using TD-DFT/B3LYP/6-31+G(d,p) for isolated dye and TD-DFT/CAM-B3LYP/6-31G(d,p)/LANL2DZ for dyes@(TiO2)9H4. The results reveal that spectra for Braz-Bd-oxane and Braze-Bd-ether complexes red-shifted compared to the individually selected dyes. The simulated absorption spectra of the adsorbed dyes on (TiO2)9H4 are red-shifted compared to the free dye. Moreover, Braz-Bd-oxane and Braz-Bd-ether exhibit better charge transfer and photovoltaic properties than the selected natural dyes forming these complexes. Based on the dyes' optoelectronic properties and photovoltaic properties, the designed molecules Braz-Bd-oxane and Braze-Bd-ether are considered better candidates to be used as photosensitizers in dye solar cells.

PRISTINE AND GROUP IV DOPED BORON NITRIDE SINGLE-WALL NANOTUBES FOR HYDROGEN STORAGE: A DENSITY FUNCTIONAL THEORY COMPUTATIONAL INVESTIGATION

In this report, a density functional theory (DFT) computational approach was used to investigate the structural and electronic properties of molecular hydrogens adsorbed on single-walled boron nitride nanotubes (BNNTs) with/without doped by group IV elements, such as carbon (C), silicon (Si), and germanium (Ge) atom. The twelve hydrogen molecules (H2) were added to the outer surfaces of BNNT frameworks. Geometry optimization calculations were performed to find the local energy minima of the BNNTs nanostructures with the molecular hydrogens at the DFT/B3LYP/6-31G level of theory. By employing single-point calculations at the B3LYP/6-31G* level of theory, the equilibrium geometric structures were then utilized to find the electronic structures of hydrogen molecules adsorbed on the surfaces of BNNT frameworks. The results showed that the bond lengths of B-N are in the range of1.44 Å – 1.48 Å. The optimized distances of hydrogen molecules from the surfaces of BNNTs were predicted to be 3.1 Å – 3.2 Å. Moreover, the computed HOMO-LUMO energies of molecular hydrogens adsorbed on the surface of BNNTs are about 2.2 eV – 4.3 eV. For the surface map of HOMO, the electron density distribution of hydrogen molecules adsorbed on the surface of pristine BNNT was localized in the N-tip. While in the case of doped BNNTs, the electron densities of HOMOs were focused on the group IV elements. The B-tips on the pristine and doped BNNTs possess the major contribution to the LUMO.

Studies on the conformation, thermodynamics, and evaporation rate characteristics of sulfuric acid and amines molecular clusters

Recent studies have proven that the presence of amines can increase aerosol formation rate. As a representative amine, trimethylamine is recognized as a significant precursor specie in the new particle formation. Although trimethylamine-containing clusters have received much attention in theoretical studies over the past few years, some information is still not understood, such as Rayleigh scattering properties and evaporation rates. In this study, the equilibrium geometric structures and thermodynamics of (H2SO4)m.(CH3)3N.(H2O)n (m = 1–2, n = 0–4) clusters were systematically investigated using density function theory M06-2X coupled with the 6–311++G(3df,3pd) basis set. The single-point energies are corrected using the DF-MP2-F12 with a VDZ-F12 basis set. For comparison, the corresponding ammonia- and dimethylamine-containing clusters are also investigated. Combined with multiple collision methods, the possible forming paths are summarized. The results indicate that base molecules play different role in the particle formation with different reaction paths. The basicity of bases mainly controls the formation of the initial cluster of acid-base. However, it is not necessarily the only determining factor influencing sulfuric acid formed new particle. The evaporation rates were also calculated. It was found that the evaporation rates of the dimethylamine-containing clusters are lower than that of the ammonia- and trimethylamine-containing clusters, except for the initial cluster of H2SO4.(CH3)3N cluster.

Explaining improved photocatalytic activity of Double-walled TiO2 Nanotube: A hybrid density functional calculation

The single-walled and double-walled TiO2 NTs rolled up with rectangular anatase (101) slab, have been investigated using modified hybrid density functional (m-B3LYP) with all-electron Gaussian basis set. We have considered single-walled and double-walled TiO2 NTs only with chirality of (0, n) and (0, m)@(0, n), respectively. Their equilibrium geometric structure, stability, electronic structure and band gap edge position relative to water splitting redox potential have been calculated. For single-walled and double-walled TiO2 NTs, the diameters and Ti-O bond lengths remain unchanged compared to TiO2 slab. To analyze the stability of TiO2 NTs, we have calculated the strain energies and formation energies which decrease with the increased diameters, and simulated the binding energies for double-walled ones to describe two walls interaction. when increasing the NTs diameters, the band gap widths of single-walled TiO2 NTs decrease with the valence band and conduction band moving downward. The double-walled TiO2 NTs exhibit II-type band structure characteristics, and their band gap widths are considerable smaller than that of single-walled ones, with the band gap edge straddling the water splitting redox potential. Based on these important findings, we can explain the mechanism of improved photocatalytic activity of double-walled TiO2 NTs as compared to the single-walled ones.

First-principles study of Bi3+ -related luminescence and traps in the perovskites CaMO3(M=Zr,Sn,Ti)

The ${\mathrm{Bi}}^{3+}$ ion is an excellent activator and sensitizer for luminescent materials. However, the complexity and variety of the ${\mathrm{Bi}}^{3+}$-related transitions bring a great challenge to the study of luminescence processes of ${\mathrm{Bi}}^{3+}$ doped materials. Here, we presented first-principles calculations to determine the excitation, relaxation, and emission processes of ${\mathrm{Bi}}^{3+}$ activated materials by using $\mathrm{Ca}M{\mathrm{O}}_{3}:{\mathrm{Bi}}^{3+}(M=\mathrm{Zr},\phantom{\rule{0.28em}{0ex}}\mathrm{Sn},\phantom{\rule{0.28em}{0ex}}\mathrm{Ti})$ as prototype systems, where ${\mathrm{Bi}}^{3+}$ substitutes ${\mathrm{Ca}}^{2+}$ in similar coordinate environments but presents tremendously different excitation and emission spectra. The equilibrium geometric structures of excited states were calculated based on density-functional theory (DFT), with appropriately constraining the electron occupation and including the spin-orbit couplings. Then the hybrid DFT calculations were carried out to obtain the electronic structures and defect levels. Different metastable excited states and Stokes shift were obtained for $M=\mathrm{Zr}$, Sn, and Ti, which explain the remarkable differences in the measured emission spectra. The energies of three types of transitions are obtained from the calculations, including intra-${\mathrm{Bi}}^{3+}$ bands transition and charge transfer between ${\mathrm{Bi}}^{3+}$ ions and the band edges. This leads to a clear and reliable interpretation of all the excitation spectra in the series. The method and its applications to $\mathrm{Ca}M{\mathrm{O}}_{3}:{\mathrm{Bi}}^{3+}$ show the potential of first-principles calculations in analyzing and predicting luminescent properties of ${\mathrm{Bi}}^{3+}$ activated materials.

Direct laser cooling schemes for the triatomic SOH and SeOH molecules based on ab initio electronic properties.

Direct laser cooling is a very promising method to obtain cold molecules for various applications. However, a molecule with satisfactory electronic and optical properties for the optical scheme is difficult to identify. By suggesting criteria for the qualified molecules, we develop a method to identify the suitable polyatomic molecules for direct laser cooling. The new criteria from the equilibrium geometrical structures and fundamental frequencies of the ground and low-lying excited states are used to replace the past ones based on Franck-Condon factors. The new method can rapidly identify the preferable one among many candidate polyatomic molecules based on ab initio calculations because the new criteria are free from the construction of potential energy surfaces. The method is testified by using triatomic molecules containing OH. All the reported and two new molecules suitable for direct laser cooling are identified by comparing 168 electronic states of 28 molecules with the new criteria. The newly found molecules have been confirmed using the Franck-Condon factors from the construction of potential energy surfaces. Finally, the optical schemes for the direct laser cooling of the SOH and SeOH molecules are established.

Spectral and quantum chemical analysis of ethyl 4-[3-(adamantan-1-yl)-4-phenyl-5-sulfanylidene-4,5-dihydro-1H-1,2,4-triazole-1-yl]methylpiperazine-1-carboxylate

The Fourier transform infrared and Raman spectra of the adamantane-based compound ethyl 4-[3-(adamantan-1-yl)-4-phenyl-5-sulfanylidene-4,5-dihydro-1H-1,2,4-triazol-1-yl]methylpiperazine-1-carboxylate were recorded in the ranges of 3200–650[Formula: see text]cm[Formula: see text] and 3200–150[Formula: see text]cm[Formula: see text], respectively. The UV/Vis spectrum of solution of the title compound in ethanol was measured in the range of 450–200[Formula: see text]nm. The DFT calculations at the B3LYP/cc-pVDZ and B3LYP/cc-pVTZ levels of the theory were performed to obtain the equilibrium geometric structure and to predict vibrational IR and Raman spectra of the title molecule. The TDDFT calculations at the CAM-B3LYP/cc-pVTZ level of the theory, as well as MRPT calculations at the CASSCF(4,5)/XMCQDPT2 level of the theory were carried out to reproduce the electronic absorption spectrum. The experimental IR, Raman and UV/Vis spectra were interpreted on the basis of results of quantum chemical modeling. Based on Mulliken and Löwdin atomic population analysis, it was established that the compound under study exhibits features of an intramolecular charge transfer.

Computational Verification of So-Called Perovskite Solar Cells as PbI64−-Aligned Solar Cells

Effective sensitizing components in so-called perovskite solar cells (PSC) are lead hexaiodide (PbI64−) salts of PbI64− (MeNH3+)n (n = 2∼4). Density-functional-theory-based molecular modeling (DFT/MM) of X-ray crystalline structure of PbI64−/MeNH3+ salt (FOLLIB) verifies that the packing unit of FOLLIB has UV/Vis absorption spectrum at λmax = 424 nm, giving pale yellow color as complementary color. DFT/MM of the horizontal component in the FOLLIB gives narrow energy gap of 0.3 eV, verifying remarkable semiconducting property through tight alignments of PbI64− components coupled with MeNH3+. DFT/MM of the central PbI64−/MeNH3+ components verifies that the central component has UV/Vis absorption spectra with respective λmax = 570 nm, λmax = 762 nm and λmax = 945 nm, and plays an essential role as panchromatic sensitizers. In addition, their equilibrium geometric structures show slightly hypsochromic UV/Vis absorption spectra at respective λmax = 486 nm, λmax = 560 nm, and λmax = 563 nm as results of migration of MeNH3+ close to PbI64−. DFT/MM also verifies that PbI64− components align tightly to nanocrystalline TiO2 (nc-TiO2) and to spiro-OMeTAD in PSC through electron density induced by van der Waals interaction. Electron density-based alignments of PbI64− components well explain unidirectional and leakage-free electron diffusion leading to high open-circuit voltage in PbI64−-aligned solar cells. At the same time, the semiconducting and panchromatic sensitizing layer of PbI64−/MeNH3+ components contribute to excellent short-circuit photocurrent of PbI64−-aligned solar cells.

Molecular clusters Cs3X3 and Cs4X4 (X = Br, I): Quantum chemical study of structure and thermodynamic properties

AbstractThe properties of trimer Cs3X3 and tetramer Cs4X4 (X = Br, I) molecules have been studied using DFT with B3LYP5 functional and MP2 and MP4 methods. Two equilibrium geometrical structures of trimers, hexagonal (D3 h) and “butterfly-shaped” (Cs), and one for tetramers, distorted cubic (Td), are confirmed to exist; geometrical parameters and vibrational spectra are determined. The relative concentration of Cs3X3 isomers has been evaluated; the butterfly-shaped isomer dominates over hexagonal in saturated vapour in a broad temperature range. The dissociation reactions through different channels have been considered and enthalpies of formation ΔfH°(0) of clusters determined:−858 ± 20 kJ mol−1 (Cs3Br3), −698 ± 20 kJ mol−1 (Cs3I3), −1270 ± 30 kJ mol−1 (Cs4Br4) and −1045 ± 30 kJ mol−1 (Cs4I4). The Gibbs free energies ∆rG°(T) calculated for the dissociation reactions of trimer and tetramer molecules have indicated that these molecules are resistive in narrow temperature range only and decompose spontaneous...

A density functional theory study on structures, stabilities, and electronic and magnetic properties of AunC (n = 1–9) clusters

The equilibrium geometric structures, relative stabilities, electronic stabilities, and electronic and magnetic properties of the AunC and Aun+1 (n=1–9) clusters are systematically investigated using density functional theory (DFT) with hyper-generalized gradient approximation (GGA). The optimized geometries show that one Au atom added to the Aun−1C cluster is the dominant growth pattern for the AunC clusters. In contrast to the pure gold clusters, the AunC clusters are most stable in a quasi-planar or three-dimensional (3D) structure because the C dopant induces the local non-planarity, with exceptions of the Au6,8C clusters who have 2D structures. The analysis of the relative and electronic stabilities reveals that the Au4C and Au6 clusters are the most stable in the series of studied clusters, respectively. In addition, a natural bond orbital (NBO) analysis shows that the charges in the AunC clusters transfer from the Aun host to the C atom. Moreover, the Au and C atoms interact with each other mostly via covalent bond rather than ionic bond, which can be confirmed through the average ionic character of the Au–C bond. Meanwhile, the charges mainly transfer between 2s and 2p orbitals within the C atom, and among 5d, 6s, and 6p orbitals within the Au atom for the AunC clusters. As for the magnetic properties of the AunC clusters, the total magnetic moments are 1μB for n=odd clusters, with the total magnetic moments mainly locating on the C atoms for Au1,3,9C and on the Aun host for Au5,7C clusters. However, the total magnetic moments of the AunC clusters are zero for n=even clusters. Simultaneously, the magnetic moments mainly locate on the 2p orbital within the C atom and on the 5d, 6s orbitals within the Au atom.

First principle calculations of physical properties for bioinformational molecule thymine

Method Hartree-Fock and density functional theory with the base set of 6-311 ++ G (d, p) were used to calculate the equilibrium geometrical structure, electronic structure and vibrational spectra of molecules for thymine. Based on analysis of simulation results showed that the investigated molecule is stable in terms of structural optimization. Calculations full and partial densities of electronic states for thymine molecules. The agreement between experimental and theoretical spectral positions, intensities of the IR and Raman bands is good.

Plane wave density functional theory studies of the structural and the electronic properties of amino acids attached to graphene oxide via peptide bonding

We studied the electronic and the structural properties of amino acids (alanine, glycine, and histidine) attached to graphene oxide (GO) by peptide bonding, via plane wave pseudopotential total-energy calculations within the local spin density approximation (LSDA). The HOMO-LUMO gap, the Hirshfeld charges, and the equilibrium geometrical structures exhibit keen variations depending on the species of the attached amino acid. The GO-amino acid system appears to be a good candidate as a biosensor.

Substituent effects on the absorption and vibrational spectra of some 2-hydroxy Schiff bases: DFT/TDDFT, natural bond orbital and experimental study

The electronic structure of salicylideneaniline (SA) and some of its derivatives are investigated both experimentally and theoretically. The equilibrium geometric structures of the studied compounds are determined at the B3LYP/6-311++G** level of theory. A set of 12 substituted SA derivatives is considered in the present work. The choice of these substituents aims to create a push-pull system on the SA basic structure which would shade light onto its photo physics. The electronic absorption spectra of SA are recorded in the UV-VIS region, in both polar and nonpolar solvents. Assignments of the observed electronic transitions are facilitated via time-dependent density functional theory (TDDFT) computations at the same level of theory. Electronic configurations contributing to each excited state are identified and the relevant MOs are characterized. The extent of delocalization and intramolecular charge transfer are estimated and discussed in terms of natural bond orbitals (NBO) analysis and second order perturbation interactions between donor and acceptor MOs. Solvent effects on the electronic absorption spectra are discussed in terms of the difference in polarizabilities of the ground and excited states. FTIR spectra of SA and its derivatives are measured in KBr platelets. Detailed vibrational assignments are given based on the calculated potential energy distributions. “IR marker bands” that characterize the SA framework are identified. The effect of substituents, the nature of the characteristic “marker bands”, and intensity quenching of some bands are discussed.

Structure and properties of molecular and ionic clusters in vapour over caesium fluoride

The properties of neutral molecules Cs2F2, Cs3F3, and Cs4F4, and positive and negative cluster ions Cs2F+, CsF2−, Cs3F2+, Cs2F3−, Cs4F3+, and Cs5F4+ were studied by several of quantum chemical methods implementing density function theory and Möller–Plesset perturbation theory of second and fourth orders. For all species, the equilibrium geometrical structure and vibrational spectra were determined. Different isomers have been revealed for the trimer neutral molecule Cs3F3; pentaatomic, both positive and negative, Cs3F2+, Cs2F3−; and heptaatomic Cs4F3+ ions. The most abundant isomers in the saturated vapour were determined. Enthalpies of dissociation reactions and enthalpies of formation of the species were obtained.

Interactions Between Sodium Ion and Constituents of Chitosan: DFT Study

Glucosamine and acetylglucosamine are the constituents of chitosan and chitin natural biopolymers. In the present study, the structure and properties of the D-glucosamine monomer (A), N-acetylglucosamine monomer (B), and ion-molecular adducts with Na⁺ cation have been explored. The equilibrium geometrical structure, vibrational spectra of the species have been determined, using the DFT/B3LYP method with the 6-31G(d) basis set. Larger basis sets up to 6-311++G(d,p) were utilized to compute energies of reactions between Na+ ion and A and B molecules. The exothermicity and spontaneous character of the adducts formation reactions have been confirmed.

Molecular and Ionic Clusters of Rubidium Fluoride: Theoretical Study of Structure and Vibrational Spectra

In this study, the geometrical structure and vibrational spectra of the trimer molecule Rb3F3 and ionic clusters Rb2F+, RbF2-, Rb3F2+, and Rb2F3- were studied by density functional theory (DFT) with hybrid functional B3P86 and Moller–Plesset perturbation theory of second order (MP2). The effective core potential with Def2–TZVP (6s4p3d) basis set for rubidium atom and aug–cc–pVTZ (5s4p3d2f) basis set for fluorine atom were used. The triatomic ions have a linear equilibrium geometric structure of D∞h symmetry, whereas for pentaatomic ions Rb3F2+, Rb<sub23F3- and trimer molecule Rb3F3 different isomers have been revealed. For the ions Rb3F2+, Rb2F3- three isomers were confirmed to be equilibrium; the linear (D∞h ), the planar cyclic (C2v ) and the bipyramidal (D3h ) while for trimer Rb3F3, two isomers were found; the hexagonal (D3h ) and the “butterfly-shaped” (C2v ) configuration.

Structural evolution and stabilities of negatively charged lead telluride clusters

The equilibrium geometric structures, relative stabilities and electronic properties of negatively charged lead telluride clusters are systematically investigated using density functional theory (DFT). The result offered both vertical and adiabatic detachment energies (VDEs and ADEs) for these clusters, divulging an outline of alternating values in which odd n clusters exhibited higher values than even n clusters. Simulations found the negatively charged lead telluride clusters with even n to be thermodynamically more stable than their immediate odd n neighbors, with a consistent pattern also being found in their HOMO–LUMO (HL) gaps. Analysis of the clusters dissociation energies found at [Formula: see text] cluster to be the preferred product of the queried fragmentation processes, consistent with our finding that [Formula: see text] cluster exhibits enhanced stability. Beyond n = 12, this study showed that the negatively charged ( PbTe )nclusters in the size range n = 13 – 20, prefer two-dimensional stacking of face-sharing lead telluride cubical units, where lead and tellurium atoms possess a maximum of five-fold coordination. The preference for six-fold coordination, which is observed in the bulk, was not observed at these cluster sizes.

Ab initio calculations of the equilibrium geometric structure of the electron's construction and the vibrational spectra of adenine molecules

Представлено результати ab initio розрахунків рівноважної геометричної будови, електронної структури та коливних спектрів для молекули аденіну. Для розрахунків використано обмежений за спіном метод Хартрі-Фока (RHF) і теорію функціоналу густини (DFT) з базисним набором 6-31. На основі аналізу результатів розрахунків встановлено, що досліджувана молекула є стабільна в умовах структурної оптимізації. Проведено розрахунки повних та парціальних густин електронних станів для молекули аденіну. Розраховані частоти та інтенсивності спектральних коливальних ліній добре узгоджуються із наявними експериментальними даними.

Structure, stability, and electronic property of carbon-doped gold clusters AunC− (n = 1–10): A density functional theory study

The equilibrium geometric structures, relative stabilities, and electronic properties of Au(n)C(-) and Au(n+1)(-) (n = 1-10) clusters are systematically investigated using density functional theory with hyper-generalized gradient approximation. The optimized geometries show that one Au atom capped on Au(n-1)C(-) clusters is a dominant growth pattern for Au(n)C(-) clusters. In contrast to Au(n+1)(-) clusters, Au(n)C(-) clusters are most stable in a quasi-planar or three-dimensional structure because C doping induces the local non-planarity while the rest of the structure continues to grow in a planar mode, resulting in an overall non-2D configuration. The relative stability calculations show that the impurity C atom can significantly enhance the thermodynamic stability of pure gold clusters. Moreover, the effect of C atom on the Au(n)(-) host decreases with the increase of cluster size. The HOMO-LUMO gap curves show that the interaction of the C atom with Au(n)(-) clusters improves the chemical stability of pure gold clusters, except for Au3(-) and Au4(-) clusters. In addition, a natural population analysis shows that the charges in corresponding Au(n)C(-) clusters transfer from the Au(n)(-) host to the C atom. Meanwhile, a natural electronic configuration analysis also shows that the charges mainly transfer between the 2s and 2p orbitals within the C atom.