Building Machine Learning systems for multi-atoms structures: CH3NH3PbI3 perovskite nanoparticles

In this study, we built a variety of Machine Learning (ML) systems over 23 different sizes of CH3NH3PbI3 perovskite nanoparticles (NPs) to predict the atoms in the NPs from their geometric locations. Our findings show that a specific type of ML algorithms, tree-based models which are Random Forest (RF), Extreme Gradient Boosting (XGBoost), Decision Trees (DT), can perfectly learn CH3NH3PbI3 perovskite NPs. Surprisingly, some popular ML algorithms such as Naive Bayes (NB), Support Vector Machines (SVM), Partial Least Squares (PLS), Regularized Logistic Regression (LR), Neural Networks (NN), Stacked Auto-Encoder Deep Neural Network (DNN), K-Nearest Neighbor (KNN) fail to learn CH3NH3PbI3 perovskite NPs

Rapidly predicting Kohn–Sham total energy using data-centric AI

Predicting material properties by solving the Kohn-Sham (KS) equation, which is the basis of modern computational approaches to electronic structures, has provided significant improvements in materials sciences. Despite its contributions, both DFT and DFTB calculations are limited by the number of electrons and atoms that translate into increasingly longer run-times. In this work we introduce a novel, data-centric machine learning framework that is used to rapidly and accurately predicate the KS total energy of anatase TiO 2 nanoparticles (NPs) at different temperatures using only a small amount of theoretical data. The proposed framework that we call co-modeling eliminates the need for experimental data and is general enough to be used over any NPs to determine electronic structure and, consequently, more efficiently study physical and chemical properties. We include a web service to demonstrate the effectiveness of our approach. © 2022, The Author(s)

Tailoring the structural properties and electronic structure of anatase, brookite and rutile phase TiO2 nanoparticles: DFTB calculations

In this study, we perform a theoretical investigation using the density functional tight-binding (DFTB) approach for the structural analysis and electronic structure of anatase, brookite and rutile phase TiO2 nanoparticles (NPs). Our results show that the number of Ti-O bonds is greater than that of O-O, while the number of Ti-Ti bonds is fewer. Thus, large amounts of O atoms prefer to connect to Ti atoms. The increase in the temperature of the NPs contributes to an increase in the interaction of Ti–O bonding, but a decrease in the O-O bonding. The segregation of Ti and O atoms shows that Ti atoms tend to co-locate at the center, while O atoms tend to reside on the surface. Increasing temperature causes a decrease of the bandgap from 3.59 to 2.62 eV for the brookite phase, which is much more energetically favorable compared to the bulk, while it could increase the bandgap from 3.15 to 3.61 eV for anatase phase. For three-phase TiO2 NPs, LUMO and Fermi levels decrease. The HOMO level of anatase phase NP decreases, but it increases for brookite and rutile phase TiO2 nanoparticles. An increase in the temperature contributes to the stabilization of anatase phase TiO2 NP due to a decrease in the HOMO energies. © 2020 Elsevier B.V

Electronic Transport and Non-linear Optical Properties of Hexathiopentacene (HTP) Nanorings: A DFT Study

The electronic structure and structural and optoelectronic properties of hexathiopentacene (HTP) nanorings have been carried out by density functional theory (DFT) and time-dependent DFT (TD-DFT). Herein, the binding energy per atom, ionization potential, electron affinity, chemical hardness, highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gap, refractive index, charge distributions, absorbance spectra and non-linear optical properties have been measured. The calculations on these nanorings show that the HOMO–LUMO gaps range from 1.87 eV to 1.28 eV, which corresponds to the bandgap of known photovoltaic semiconductors, while the absorbance spectrum increases from 674 nm (1.84 eV) to 874 nm (1.42 eV), which indicates that the HTP nanorings absorb more light as the nanoring size is increased. From the binding energy, the stability of the HTP nanorings is higher than that of the HTP structure. Our results show that an increase in the size may play a significant role in improving the design of optoelectronic devices based upon these HTP nanorings. © 2020, The Minerals, Metals & Materials Society

Electronic structures and bonding of graphdiyne and its BN analogs: Transition from quasi-planar to planar sheets

We demonstrate a possible structural transition from graphdiyne (GDY) to boron nitride (BN)-diyne (C90-18n(BN)9nH18; n = 0-5) sheets using the density functional theory (DFT). The aim of this study is to investigate the effects of substitution of carbon atoms by B and N atoms on structural, electronic and reactivity properties. We found that a structural transition from quasi-planar to planar occurs at n = 2. The stability decreases with increasing the number of B/N. Moreover, the pristine BNdiyne is only less stable than pristine GDY by about 0.92 eV/atom. Our calculations also show that the energy gap (Eg) of the GDY and its BN structural analog models changes in the wide range of 0.45–5.52 eV as the number of B and N atoms increases in the system. The Eg of the BNdiyne (n = 5) is found to be 5.52 eV, indicating electrically an insulating behavior, however, it is 0.45 eV for the BNdiyne (n = 4) which is higher conductivity than that of pristine GDY. Molecular dynamics simulations show that temperature induces a decrease in the Eg due to variations of the bond energy and deformation in the structures under heat treatment. The ELF analysis also confirms that the B–N bonds in new GDY-like BN sheets potentially exhibit covalent characteristics. Our results herein show that new BNdiyne sheets can be used in promising applications from chemical nanosensors to solar cell applications. © 2020 Elsevier B.V

Size‑dependent adsorption performance of ZnO nanoclusters for drug delivery applications

We have investigated the size-dependent adsorption performance of ZnO nanoclusters (NCs) as drug delivery carriers for the first time. Our results show that the adsorption energy of the favipiravir drug on the ZnO NCs is predicted in the range of - 26.69 and - 34.27 kcal/mol. The adsorption energy (- 34.27 kcal/mol) between (ZnO)(18) NC and the favipiravir is energetically desirable and more favorable than the other interactions. The size of ZnO NCs and the position of the favipiravir on the ZnO NCs cause a decrease in the energy gap, which makes the charge-transfer process easier. The bonds between O-Zn, N-Zn, and F-Zn atoms exhibit dual covalent and ionic natures. The non-covalent interaction analysis shows that the strongest H-bonds are observed near NH2 within the favipiravir molecule. Finally, the acquired results show that the interaction of ZnO NCs with the favipiravir anticancer drug can have the potential as drug delivery carriers

Zinc oxide nanoclusters and their potential application as CH4 and CO2 gas sensors: Insight from DFT and TD-DFT

We have investigated the adsorption of CH4 and CO2 gases on zinc oxide nanoclusters (ZnO NCs) using density functional theory (DFT). It was found that the CH4 tends to be physically adsorbed on the surface of all the ZnO NCs with adsorption energy in the range −11 to −14 kcal/mol. Even though, the CO2 is favorably chemisorbed on the Zn12O12 and Zn15O15 NCs, with adsorption energy about −38 kcal/mol at B3LYP/6-311G(d,p) level of theory. When the CH4 and CO2 gases are adsorbed on the ZnO NCs, their electrical conductivities are decreased, and thus the studied ZnO NCs do not generate an electrical signal in the presence of CH4 and CO2 gases. Interestingly, both pure and gas adsorbed Zn22O22 NC exhibited more favorable electronic and reactive properties than other NCs. Comparison of the structural, electronic, and optical data predicted by DFT/B3LYP and TD-DFT/CAM-B3LYP calculations with those experimentally obtained show good agreement. © 2022 Wiley Periodicals LLC

The electronic structure, transport and structural properties of nitrogen-decorated graphdiyne nanomaterials

We focus on a theoretical investigation using the DFT and LC-SCC-DFTB for investigating the structural, optical and reactivity properties and electronic structure of pristine graphdiyne (GDY) and nitrogen (N)-doped hexagonal carbon rings of GDY nanomaterials. Our calculations show that the energy gap (E-g) of the GDY is 1.00 eV which is excellent agreement with the DFTB. By increasing the content of N, the E-g changes in the wide range of 0.15-0.98 eV. The absorbance maxima are at 1.91 eV (647 nm) for the GDY, 1.46 eV (845 nm) for the N-GDY, 2.15 eV (576 nm) and 1.21 eV (1020 nm). The decrease in the value of the E-g with temperature for the GDY and 3 N GDY is observed due to variations of the bond energy which reflects the E-g. However, an increase in the value of the E-g with temperature is found linearly for the N-GDY because the Fermi energy level is pushed higher from -3.722 to -4.027 eV. The dipole moment increases when increasing the content of N and temperature. Obtained results herein suggest the GDY and N-doped GDY nanomaterials can be used as very promising advancements for potentially useful optoelectronic novel applications. (C) 2020 Elsevier B.V. All rights reserved

Size dependence in the electronic and optical properties of a BN analogue of two-dimensional graphdiyne: A theoretical study

In this study, we propose a new type of a BN analogue of two-dimensional (2D) graphdiyne. By DFTB, we carried out the changes in the electronic and optical properties of BNdiyne based on size. Higher binding energies with increase size ensure an increase in the stability of BNdiyne. Considerable decrease in the energy gap from 1.09 eV to 0.02 eV suggests BNdiyne transforms from a semiconductor to metal, thus an increase in electrical conductivity. The HOMO energy of BNdiyne with size contributes the stability. The increase in the size induces a decrease in adiabatic electron affinity and chemical hardness, but an increase in the refractive index, adiabatic ionization potential, electrophilicity index and maximum amount electronic charge index which enhance the energy stability of the BNdiyne during charge transfer. These findings herein indicate that new 2D-BNdiyne can be used in promising applications from nanosensors to solar cell applications. © 2020 Elsevier B.V

3d-transition metals (Cu, Fe, Mn, Ni, V and Zn)-doped pentacene π-conjugated organic molecule for photovoltaic applications: DFT and TD-DFT calculations

In this study, we have performed a thorough examination of density functional theory (DFT) and time-dependent (TD) DFT to investigate the structural and optoelectronic properties of 3d-transition metals (Cu, Fe, Mn, Ni, V and Zn)-doped pentacene π-conjugated organic molecule. The HOMO energy level of Ni-doped pentacene is − 6.17 eV wide, i.e., about 1.31 eV greater and more negative than pentacene. The bandgap of the pentacene considerable decreases from 2.20 eV to 1.32, 1.35 and 0.37 eV, for Mn, Zn and V-doped pentacene structures, respectively, which affords an efficient charge transfer from HOMO to LUMO. The HOMO–LUMO energy gap is higher (4.44 eV, for Ni-doped pentacene), implying that the kinetic energy is higher and high chemical reactivity. We have examined, additionally, the reactivity and absorption properties of individual undoped and 3d-transition metals-doped pentacene. Pentacene has the largest vertical ionization potential (6.18 eV), corresponding to the highest chemical stability. Our results suggest that the new 3d-transition metals-doped pentacene may significantly contribute to the efficiency of solar cells. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature