Jacek A. Majewski

We investigated quantum chemical parameters for single-molecule magnets using theoretical calculations using the density functional theory (DFT), which includes the Hubbard component (PBE+U). An investigation is conducted into the transition metal phthalocyanine molecules TM-Pc (3d transition metal with TM = Ti, Cr, Mn, Co, and Cu). The energy of the frontier molecular orbitals, gap (HOMO-LUMO), electronegativity, chemical potential, global hardness, softness, and electrophilicity index are among the electronic characteristics and reactivity indices associated with TM-Pc molecules that are displayed. These characteristics are intended to help comprehend and predict the future course of innovative experimental research. As a result, the suggested materials exhibit promising properties for spintronic applications.

To speed up the implementation of the two-dimensional materials in the development of potential biomedical applications, the toxicological aspects toward human health need to be addressed. Due to time-consuming and expensive analysis, only part of the continuously expanding family of 2D materials can be tested in vitro. The machine learning methods can be used—by extracting new insights from available biological data sets, and provide further guidance for experimental studies. This study identifies the most relevant highly surface-specific features that might be responsible for cytotoxic behavior of 2D materials, especially MXenes. In particular, two factors, namely, the presence of transition metal oxides and lithium atoms on the surface, are identified as cytotoxicity-generating features. The developed machine learning model succeeds in predicting toxicity for other 2D MXenes, previously not tested in vitro, and hence, is able to complement the existing knowledge coming from in vitro studies. Thus, we claim that it might be one of the solutions for reducing the number of toxicological studies needed, and allows for minimizing failures in future biological applications.

Theoretical studies of morphology, stability, and electronic structure of monolayer hexagonal CBN alloys with rich content of h‐BN and carbon concentration not exceeding 50% are presented. The studies are based on the bond order type of the valence force field to account for the interactions between atomic constituents and Monte Carlo method with Metropolis algorithm to establish equilibrium distribution of atoms over the lattice. It is found that the phase separation into graphene and h‐BN domains occurs in the majority of growth conditions. Only in N‐rich growth conditions, it is possible to obtain a quasi uniform distribution of carbon atoms over the boron sublattice. It is been predicted that the energy gap in stoichiometric C_x(BN)_1−x alloys exhibits extremely strong bowing.

The magnetic characteristics of a series of borohydride‐based systems, including binary α‐/β‐Ln(BH₄)₃ phases (Ln = Gd, Tb, Dy, Ho, Er, and Tm) with direct Ln–HBH–Ln bridges and selected mixed‐metal systems, LiYb(BH₄)₄, NaYb(BH₄)₄, KHo(BH₄)₄, RbTm(BH₄)₄, with isolated Ln³⁺ ions embedded in [Ln(BH₄)₄]^– anions are described for the first time using SQUID magnetometry and DFT+U calculations. Crystal field effects as well as the nature and strength of magnetic superexchange interactions via BH₄^– ligands are established based on a ligand field theory approach. We find Auzel's scalar crystal field strength parameter (Nv, the weighted quadratic mean of the ligand field parameters B_k^q) for these systems to be substantial, in particular for α‐Ho(BH₄)₃, indicating a significant covalent component in the Ho···H bonding. The BH₄^– anion is capable of mediating both weakly ferro‐ or antiferromagnetic superexchange. Quantum mechanical DFT+U calculations, even when including spin‐orbit coupling effects, do not reliably describe the sign and the size of the magnetic superexchange constants in these systems.

We study the dissociative adsorption of methane at the surface of graphene. Free energy profiles, which include activation energies for different steps of the reaction, are computed from constrained ab initio molecular dynamics. At 300 K, the reaction barriers are much lower than experimental bond dissociation energies of gaseous methane, strongly indicating that the graphene surface acts as a catalyst of methane decomposition. On the other hand, the barriers are still much higher than on the nickel surface. Methane dissociation therefore occurs at a higher rate on nickel than on graphene. This reaction is a prerequisite for graphene growth from a precursor gas. Thus, the growth of the first monolayer should be a fast and efficient process while subsequent layers grow at a diminished rate and in a more controllable manner. Defects may also influence reaction energetics. This is evident from our results, in which simple defects (Stone-Wales defect and nitrogen substitution) lead to different free energy landscapes at both dissociation and adsorption steps of the process.

Graphene, a 2-dimensional monolayer form of sp2 hybridizated carbon atoms, is attracting increasing attention due to its unique and superior physicochemical properties. Covalently functionalized graphene layers, with their modifiable chemical functionality and usefull electrical properties, are excellent candidates for broad range of sensors, suitable for biomedical, optoelectronic and environmental applications. Here, we present extensive study of transport properties of sensors based on covalently functionalized graphene monolayer (GML) with graphene electrodes. The transmissions, density of states and current-voltage characterisctics supported by analysis of charge distribution of GML functionalized by -CH3, -CH2, -NH2, -NH and -OH fragments have been calculated by means of density functional theory (DFT) and non-equilibrium Green's function (NEGF). Further, we demonstrate how to control the device sensitivity by manipulating: (i) concentration, (ii) particular arrangement, and (iii) type of surface groups. We explain the underlying detection physical mechanisms. Comparisons of the theoretical results to available experimental data are provided are made and show good agreement.

We present exemplary results of extensive studies of mechanical, electronic and transport properties of covalent functionalization of graphene monolayers (GML) with -NH2. We report new results of ab initio studies of covalent functionalization of GML with -NH2 groups up to 12.5% concentration. Our studies are performed in the framework of the density functional theory (DFT) and non-equilibrium Green's function (NEGF). We discuss the stability (adsorption energy), elastic moduli, electronic structure, band gaps, and effective electron masses as a function of the density of the adsorbed molecules. We also show the conductance and I(V) characteristic of these systems. Generally, the stability of the functionalized graphene layers decreases with the growing concentration of attachments and we determine the critical density of the molecules that can be chemisorbed on the surface of GLs. Because of local deformations of GLs and sp3 rehybridization of the bonds induced by fragments, elastic moduli decrease with increasing number of groups. Simultaneously, we observe that the functionalizing molecules stretch the graphenes lattice, the effect being more pronounced for higher concentration of adsorbed molecules. We find out that the GLs functionalization leads in many cases to the opening of the graphene band gap (up to 0.5302 eV for 12.5% concentration) and can be therefore utilized in graphene devices. The new HOMO and LUMO originate mostly from the impurity bands induced by the functionalization and they exhibit parabolic dispersion with electron effective masses comparable to ones in silicon or gallium nitride.

We study the effects of covalent functionalization of single wall carbon nanotubes (CNT) on their elastic properties. We consider simple organic molecules –NH, –NH₂, –CH₂, –CH₃, –OH attached to CNTs' surface at various densities. The studies are based on the first principles calculations in the framework of density functional theory. We have determined the changes in the geometry and the elastic moduli of the functionalized CNTs as a function of the density of adsorbed molecules. It turns out that elastic moduli diminish with increasing concentration of adsorbents, however, the functionalized CNTs remain strong enough to be suitable for reinforcement of composites. The strongest effect is observed for CNTs functionalized with –CH₂ radical, where the Young's modulus of the functionalized system is 30% smaller than in the pristine CNTs.