arXiv subjects

Ana S. Dobrota

Publications and source records attributed to Ana S. Dobrota.

15 recordsLinked to original sources

arXiv2026

Engineering Electrochromism in Ni-Deficient NiO through Defect, Dopant, and Strain Coupling

The electrochromic response of Ni-deficient NiO is governed by vacancy-mediated electronic processes that can be strongly influenced by dopant chemistry and lattice deformation. Using density functional theory, we systematically investigated Cu-, Sn-, and V-doped Ni-deficient NiO(001) surfaces and examined alkali-ion insertion at surface Ni vacancies. Li insertion proceeds as nearly complete ionic electron donation (~+0.9 e), but the fate of the injected electron depends on dopant identity. V-doping preserves framework-dominated charge compensation and leads to conventional bleaching through filling of vacancy-associated hole states. In contrast, Sn actively traps the injected charge, generating dopant-assisted optical transitions and reversing the electrochromic response, while Cu produces an intermediate spectral redistribution without significant dopant reduction. Substitution of Li by Na or K in the V-doped system does not alter the switching mechanism, confirming that vacancy-state filling governs the optical behavior. Biaxial tensile strain enhances the energetics of Li insertion but reduces optical contrast by altering the defect electronic structure. These results establish dopant activity, vacancy stabilization, and lattice strain as key parameters controlling electrochromism in NiO-based materials.

cond-mat.mtrl-sci↗

arXiv2026

A DFT study of B-doped graphene as a metal-anchor: effects of oxidation and strain

In this work, we present a systematic DFT investigation of the interaction between B-doped graphene and four selected metals: Mg and Zn, relevant for next-generation metal-ion batteries, and Cu and Pt, important for single-atom catalysis. Three different boron doping concentrations were considered to elucidate how dopant density influences the binding strength, charge transfer, and electronic structure of the resulting systems. In addition, the effects of biaxial strain and surface oxidation were examined to assess their impact on the reactivity and stability of B-doped graphene. The results show that boron doping substantially enhances graphene's affinity toward metal adsorption, though the extent and nature of this effect depend strongly on the metal type and doping level. For some of the metals investigated, the interaction is found to be almost entirely charge-transfer driven, with minimal orbital hybridization. Mechanical strain is found to enable fine-tuning of the metal/substrate interaction, while surface oxidation introduces a more pronounced effect by enabling direct interaction between metal atoms and oxygen functional groups in most cases, thereby significantly altering adsorption geometry and strength. These findings provide valuable insights into the design of boron-doped graphene materials for energy conversion and storage applications.

cond-mat.mtrl-sci↗

arXiv2026

Defect-Engineered h-BN as a Platform for Single-Atom HER Catalysts: Descriptor Screening Refined by Electrochemical Stability Analysis

Defect engineering enables hexagonal boron nitride (h-BN) to act as a platform for stabilizing isolated metal atoms, yet systematic identification of catalytically viable motifs remains limited. Here, density functional theory is used to screen transition and coinage metals anchored at B, N, and BN vacancies in h-BN for hydrogen evolution reaction (HER) activity. Cohesive-energy benchmarking reveals that B vacancies provide the strongest thermodynamic stabilization of single atoms, while electronic-structure analysis demonstrates vacancy-dependent modulation of conductivity and metal charge state. Hydrogen adsorption free energies identify Cu@VN and Pd@VB as near-thermoneutral candidates comparable to Pt(111). However, incorporation of electrochemical stability through Pourbaix analysis significantly refines this selection: Cu@VN is unstable at low pH and susceptible to OHads poisoning, whereas Pd@VB remains stable and catalytically accessible across a broad potential-pH range. These results show that descriptor-based HER screening can generate an expanded pool of candidates, but rigorous electrochemical filtering is essential to identify truly robust systems. The presented multi-step strategy provides a general framework for rational discovery of single-atom catalysts on defect-engineered 2D supports.

cond-mat.mtrl-sci↗

arXiv2026

Single-Atom Adsorption on h-BN along the Periodic Table of Elements: From Pristine Surface to Vacancy-Engineered Sites

The adsorption of single atoms on pristine and defected hexagonal boron nitride (h-BN) was systematically investigated using density functional theory. Elements from the first three rows of the periodic table, together with selected transition and coinage metals, were examined on the pristine surface and at boron- and nitrogen-vacancy sites. On pristine h-BN, adsorption is generally weak and dominated by dispersion forces, with measurable chemisorption limited to highly electronegative atoms such as C, O, and F. The introduction of vacancies transforms h-BN into a chemically active material, increasing adsorption energies by one to two orders of magnitude. The boron vacancy strongly stabilizes metallic and electropositive species through coordination to undercoordinated nitrogen atoms, whereas the nitrogen vacancy selectively binds electronegative and covalent adsorbates. Scaling of adsorption energies with elemental cohesive energies distinguishes regimes of physisorption, chemisorption, and substitutional stabilization. These insights provide a unified description of adsorption trends across the periodic table and establish defect engineering as an effective strategy for tailoring the catalytic, sensing, and electronic properties of h-BN.

cond-mat.mtrl-sci↗

arXiv2023

Reactivity of Stone-Wales defect in graphene lattice -- DFT study

Understanding the reactivity of carbon surfaces is crucial for the development of advanced functional materials. In this study, we systematically investigate the reactivity of graphene surfaces with the Stone-Wales (SW) defect using Density Functional Theory calculations. We explore the atomic adsorption of various elements, including rows 1-3 of the Periodic Table, potassium, calcium, and selected transition metals. Our results demonstrate that the SW defect enhances binding with the studied adsorbates when compared to pristine graphene, with carbon and silicon showing the most significant differences. Additionally, we examine the effects of mechanical deformation on the lattice by constraining the system with the SW defect to the pristine graphene cell. Interestingly, these constraints lead to even stronger binding interactions. Furthermore, for carbon, nitrogen, and oxygen adsorbates, we observe that mechanical deformation triggers the incorporation of adatoms into the carbon bond network, leading to the reorganization of the SW defect structure. This work establishes a foundation for future studies in the defect and strain engineering of graphene, opening avenues for developing advanced materials and catalysts with enhanced reactivity and performance.

cond-mat.mtrl-sci↗

arXiv2023

Boron-doped graphene -- DFT study of the role of dopant concentration and oxidation on sodium and aluminium storage applications

Graphene is thought to be a promising materials for many applications. However, pristine graphene is not suitable for most electrochemical devices, where defect engineering is crucial for its performance. We demonstrate how boron doping of graphene can alter its reactivity, electrical conductivity and potential application for sodium and aluminium storage, with the emphasis on novel metal-ion batteries. Using DFT calculations, we investigate both the influence of boron concentration and the oxidation of the material, on the mentioned properties. It is demonstrated that the presence of boron in graphene increases its reactivity towards atomic hydrogen and oxygen-containing species, in other words, it makes B-doped graphene more prone to oxidation. Additionally, the presence of these surface functional groups significantly alters the type and strength of the interaction of Na and Al with the given materials. Boron-doping and oxidation of graphene is found to increase Na storage capacity of graphene by the factor of up to 4.

cond-mat.mtrl-sci↗

arXiv2021

Surface Pourbaix plots of M@N4-graphene single-atom electrocatalysts from Density Functional Theory thermodynamic modelling

Single-atom catalysts (SACs) are rapidly developing in various application areas, including electrocatalysis of different reactions, usually taking place under harsh pH-electrode potential conditions. Thus, a full atomic-level understanding of the nature of the active sites under realistic electrochemical conditions is needed, having in mind that the state of SACs active centers could be altered by the adsorption of spectating species. In this contribution, Density Functional Theory is employed to conduct thermodynamic analysis of SACs with metal atoms (Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt, or Au) embedded into N4 moiety in graphene. Various surface electrochemical processes on such SACs are considered, their Pourbaix plots are constructed, and their activity, selectivity, and stability under operating conditions are discussed. It is demonstrated how adsorption of H, O and OH can cause blockage and restructuring of the active sites and alter the electronic structure. Furthermore, when one deals with metals with lower d-band filling, it is shown that metal center oxidation is preferred over the oxidation of carbon lattice. The effect of the state of the metal center on the reactivity of the carbon lattice is discussed in the case of Fe@N4-graphene. Finally, a possible strategy for confirming the changes in the architecture of the SACs' active site by analyzing their vibration spectra is suggested.

cond-mat.mtrl-sci↗

arXiv2021

Electrochromism of Ni-deficient nickel oxide -- Theoretical justification

The development of new electrochromic materials and devices, like smart windows, has an enormous impact on the energy efficiency of modern society. One of the crucial materials in this technology is nickel-oxide. Ni-deficient NiO shows anodic electrochromism whose mechanism is still under debate. Using DFT+U calculations, we show that Ni vacancy generation results in the formation of hole polarons localised at the two oxygens next to the vacancy. Upon Li insertion or injection of an extra electron into Ni-deficient NiO, one hole gets filled, and the hole bipolaron is converted into a hole polaron well-localized at one O atom. Furthermore, the calculated absorption coefficients demonstrate that Li insertion/extraction or rather the addition/removal of an extra electron into Ni-deficient NiO can lead to switching between the oxidized (colored) and the reduced (bleached) states. Hence, our results suggest a new mechanism of Ni-deficient NiO electrochromism not related to the Ni2+/Ni3+ transition but based on the formation and annihilation of hole polarons in oxygen p-states.

cond-mat.mtrl-sci↗

arXiv2021

Aluminium storage using nitrogen-doped graphene nanoribbons from first principles

Pristine graphene interacts relatively weakly with Al, which is a specie of importance for novel generations of metal-ion batteries. We employ DFT calculations to explore the possibility of enhancing Al interaction with graphene. We investigate non-doped and N-doped graphene nanoribbons, address the impact of the edge sites, which are always present to some extent in real samples, and N-containing defects on the material's reactivity towards Al. The results are compared to that of pristine graphene. We show that introduction of edges does not affect the energetics of Al adsorption significantly by itself. On the other hand, N-doping of graphene nanoribbons is found to affect the adsorption energy of Al to the extent that strongly depends on the type of N-containing defect. While graphitic and pyrrolic N induce minimal changes, the introduction of edge NO group and doping with in plane pyridinic N result in Al adsorption nearly twice as strong as on pristine graphene. The obtained results could guide the further design of advanced materials for Al-ion rechargeable batteries.

cond-mat.mtrl-sci↗

arXiv2020

Theoretical analysis of doped graphene as cathode catalyst in Li-O2 and Na-O2 batteries -- the impact of the computational scheme

Understanding the reactions in M-O2 cells (M = Li or Na) is of great importance for further advancement of this promising technology. Computational modelling can be helpful along this way, but an adequate approach is needed to model such complex systems. We propose a new scheme for modelling processes in M-O2 cells, where reference energies are obtained from high-level theory, CCSD(T), while the interactions of reaction intermediates with catalyst surfaces are extracted from computationally less expensive DFT. The approach is demonstrated for the case of graphene-based surfaces as model catalysts in Li-O2 and Na-O2 cells using the minimum viable mechanism. B-doped graphene was identified as the best catalyst among considered surfaces, while pristine graphene performs poorly. Moreover, we show that the inclusion of dispersion corrections for DFT has a significant impact on calculated discharge and charge potentials and suggests that long-range dispersion interactions should always be considered when graphene-based materials are modelled as electrocatalysts. Finally, we offer general guidelines for designing new ORR catalysts for M-O2 cells in terms of the optimization of the interactions of catalyst surface with reaction intermediates.

cond-mat.mtrl-sci↗

arXiv2019

Altering the reactivity of pristine, N- and P-doped graphene by strain engineering: a DFT view on energy related aspects

For carbon-based materials, in contrast to metal surfaces, the relationship between strain and reactivity is not yet established, even though there are literature reports on strained graphene. Knowledge of such relationships would be extremely beneficial for understanding the reactivity of graphene-based surfaces and finding optimisation strategies which would make these materials more suitable for targeted applications. Here we investigate the effects of compressive and tensile strain (up to +/-5%) on the structure, electronic properties and the reactivity of pure, N-doped and P-doped graphene, using DFT calculations. We demonstrate the possibility of tuning the topology of the graphene surface by strain, as well as by the choice of the dopant atom. The reactivity of (doped) strained graphene is probed using H and Na as simple adsorbates of great practical importance. Strain can both enhance and weaken H and Na adsorption on (doped) graphene. In case of Na adsorption, a linear relationship is observed between the Na adsorption energy on P-doped graphene and the phosphorus charge. A linear relationship between the Na adsorption energy on flat graphene surfaces and strain is found. Based on the adsorption energies and electrical conductivity, potentially good candidates for hydrogen storage and sodium-ion battery electrodes are discussed.

cond-mat.mtrl-sci↗

arXiv2018

Sodium storage via single epoxy group on graphene - The role of surface doping

Due to its unique physical and chemical properties, graphene is being considered as a promising material for energy conversion and storage applications. Introduction of functional groups and dopants on/in graphene is a useful strategy for tuning its properties. In order to fully exploit its potential, atomic-level understanding of its interaction with species of importance for such applications is required. We present a DFT study of the interaction of sodium atoms with epoxy-graphene and analyze how this interaction is affected upon doping with boron and nitrogen. We demonstrate how the dopants, combined with oxygen-containing groups alter the reactivity of graphene towards Na. Dopants act as attractors of epoxy groups, enhancing the sodium adsorption on doped oxygen-functionalized graphene when compared to the case of non-doped epoxy-graphene. Furthermore, by considering thermodynamics of the Na interaction with doped epoxy-graphene it has been concluded that such materials are good candidates for Na storage applications. Therefore, we suggest that controlled oxidation of doped carbon materials could lead to the development of advanced anode materials for rechargeable Na-ion batteries.

cond-mat.mtrl-sci↗

arXiv2017

Atomic adsorption on graphene with a single vacancy: systematic DFT study through the Periodic Table of Elements

Vacancies in graphene present sites of altered chemical reactivity and open possibilities to tune graphene properties by defect engineering. The understanding of chemical reactivity of such defects is essential for successful implementation of carbon materials in advanced technologies. We report the results of a systematic DFT study of atomic adsorption on graphene with a single vacancy for the elements of rows 1 to 6 of the Periodic Table of Elements (PTE), excluding lanthanides. The calculations have been performed using PBE, long-range dispersion interaction-corrected PBE (PBE+D2 and PBE+D3) and non-local vdW-DF2 functional. We find that most elements strongly bind to the vacancy, except for the elements of groups 11 and 12, and noble gases, for which the contribution of dispersion interaction to bonding is most significant. The strength of the interaction with the vacancy correlates with the cohesive energy of the elements in their stable phases: the higher the cohesive energy is the stronger bonding to the vacancy can be expected. As most atoms can be trapped at the SV site we have calculated the potentials of dissolution and found that in most cases the metals adsorbed at the vacancy are more "noble" than they are in their corresponding stable phases.

cond-mat.mtrl-sci↗

arXiv2017

Atomic adsorption on pristine graphene along the Periodic Table of Elements - From PBE to non-local functionals

The understanding of atomic adsorption on graphene is of high importance for many advanced technologies. Here we present a complete database of the atomic adsorption energies for the elements of the Periodic Table up to the atomic number 86 (excluding lanthanides) on pristine graphene. The energies have been calculated using the projector augmented wave (PAW) method with PBE, long-range dispersion interaction corrected PBE (PBE+D2, PBE+D3) as well as non-local vdW-DF2 approach. The inclusion of dispersion interactions leads to an exothermic adsorption for all the investigated elements. Dispersion interactions are found to be of particular importance for the adsorption of low atomic weight earth alkaline metals, coinage and s-metals (11th and 12th groups), high atomic weight p-elements and noble gases. We discuss the observed adsorption trends along the groups and rows of the Periodic Table as well some computational aspects of modelling atomic adsorption on graphene.

cond-mat.mtrl-sci↗

arXiv2017

Lattice mismatch as the descriptor of segregation, stability and reactivity of supported thin catalyst films

Increasing demand and high prices of advanced catalysts motivate a constant search for novel active materials with reduced content of noble metals. The development of thin films and core-shell catalysts seem to be a promising strategy along this path. Using Density Functional Theory we have analyzed a number of surface properties of supported bimetallic thin films with composition A3B (where A = Pt, Pd, B = Cu, Ag, Au). We focus on surface segregation, dissolution stability and surface electronic structure. We also address the chemisorption properties of Pd3Au thin films supported by different substrates, by probing the surface reactivity with CO. We find a strong influence of the support in the case of mono- and bilayers, while the surface strain seems to be the predominant factor in determining the surface properties of supported trilayers and thicker films. In particular, we show that the studied properties of the supported trilayers can be predicted from the lattice mismatch between the overlayer and the support. Namely, if the strain dependence of the corresponding quantities for pure strained surfaces is known, the properties of strained supported trilayers can be reliably estimated. The obtained results can be used in the design of novel catalysts and predictions of the surface properties of supported ultrathin catalyst layers.

cond-mat.mtrl-sci↗