Magnesium (Mg) is known for its biocompatibility in degradable body implants, with mechanical properties similar to bone tissue. Pure Mg corrodes too fast for implants, but alloying or coating are methods to slow down the implant surface degradation. Using density functional theory calculations we study the adsorption on Mg(0001) of amino acids glycine (Gly), proline (Pro), and hydroxyproline (Hyp), and a short Gly-Hyp-Pro string. The amino acids are native to the body, form the main amino acid content of collagen, and may by adsorption form nucleation points for coating layers on the surface. We also investigate how binding of the functional groups of Hyp are affected when Mg(0001) is sparsely alloyed with zinc, lithium, calcium or aluminium, and when an aqueous environment is modelled by changing the dielectric constant near the surface from vacuum to the value of water. We find good adhesion of the amino acids overall, and find that the binding improves on alloyed surfaces.

Magnesium (Mg) has mechanical properties similar to bone tissue, and Mg ions take part in the metabolism. This makes Mg of interest for biocompatible degradable body implants, provided that its high corrosion rate can be inhibited. Slightly alloying Mg and adding surface coatings can slow down the corrosion processes without significantly changing the mechanical properties. Use of coating molecules that are native to the body increase the likelihood of making the surface biocompatible, for example by use of amino acids. We here present a density functional theory (DFT) study of the adsorption on Mg(0001) of the amino acids glycine, L-proline, and L-hydroxyproline (Hyp), the main amino acid content of collagen. We investigate how binding of the functional groups of Hyp are affected when Mg(0001) is slightly alloyed with zinc, lithium or aluminium, and we also model the immersion of the systems in a water environment to see how this affects the binding.

Understanding photophysical properties of DNA is important: it can help us elucidate and probe the impact of charges and free radicals in the cellular environment. For example, a photoemission at a given nucleobase means that we both charge it and place an electron right next to a neighboring part of the genetic code. Inverse photoemission means that we trap a free electron (at some empty state or resonance), and instead emit a low-energy photon. This may reduce the damage if it happens at an already charged base, but it can cause extra damage if it arises somewhere else. Predicting the nature of sudden optically-driven excitations, termed quasi-particles (QPs), help us detail interactions and possibly control the damage that might follow. Also, these QPs contain information on the larger DNA assembly because they reflect the fingerprints of nucleobase polarity, the hydrogen bonding in Watson-Crick pairs, and the van der Waals (vdW) interactions in the Watson-Crick-pair stacking that makes up the genome. In this study, we utilize the recently developed (optimally tuned) range-separated hybrid vdW density functional, AHBR-mRSH* [E. Schröder, R. Quintero-Monsebaiz, Y. Jiao and P. Hyldgaard, J. Phys.: Condens. Matter, 2025, 37, 211501] to analyze the electron-attached and ionized QP states of these DNA components, with a particular focus on dipole- and multipole-trapped empty states (bound or resonances). We also evaluate critical properties such as dipole and quadrupole moments, QP HOMO-LUMO energy gaps, and transition-dipole moments. Finally, we classify the Watson-Crick stacked dimers based on their QP nature. This classification provides the foundation for proposing a model of DNA reactivity and photo-physical activity.

Hydroxyapatite (HA) on a magnesium (Mg) surface is studied using density functional theory, to help understand the effect of HA coating and alloying in the surfaces of Mg-based biodegradable implants. We determine the adsorption energies and structural changes of a single layer of HA on pure Mg(0001) and on sparsely calcium (Ca) or zinc (Zn) doped Mg(0001) and find that both Zn and Ca doping improves the adsorption, except in a few positions of HA relative to the dopant position. All adsorption configurations, whether with pure or doped Mg surfaces, show deformation of the surface and HA layer. For Ca doping, we found that for a certain adsorption configuration, the dopant Ca atom moves out of the Mg surface and into the HA layer, leaving behind a Mg vacancy in the top layer of the Mg surface. Plots of electron density changes show that electrons accumulate around the Ca dopant and the neighboring Mg atoms, while in Zn doping this is less pronounced. Overall, our results demonstrate that the dopant choice and relative position of HA influence the interaction between HA and Mg-surfaces, and affect both adsorption energies and atomic and electronic structures.

Density functional theory is used to investigate the interactions between a layer of magnesium hydroxide, Mg(OH)2, the magnesium (Mg) surface Mg(0001), and the three amino acids glycine, proline, and glutamine. The aim is to improve the understanding of Mg behavior in biologically relevant environments, such as the ones that biodegradable implants experience in the body. For a simple model of such conditions, the adsorption of amino acids is studied. With the layer of Mg(OH)2 as a model of either slightly corroded Mg or intentionally coated Mg, the interfacial interaction between a layer of Mg(OH)2 and Mg(0001) is first examined in the absence of the molecules. Then follows analyses that include amino acids on top of the Mg(OH)2 layer. We find that the Mg(OH)2/Mg(0001) interaction is weak and that the layer of Mg(OH)2 can readily slide across the Mg surface. The presence of amino acids is found to have a limited influence on the adsorption of Mg(OH)2 on Mg(0001), decreasing the binding by at most 3%, while more layers of Mg(OH)2 strengthen the Mg(OH)2/Mg(0001) binding by 13%. This is still less than the binding of Mg(OH)2 layers within its native bulk structure, and our findings indicate that only a small number of hydroxide layers are required before it is energetically more favorable for Mg(OH)2 to create bulk than to stay on Mg(0001) as single layers. This provides insight into early-stage surface processes relevant for magnesium-based implant materials.

Producing large-area single-crystalline graphene is key to realizing its full potential in advanced applications, including twistronics. Yet, controlling graphene growth kinetics to avoid grain boundaries or multilayer growth remains challenging. Here, we demonstrate the possibility to obtain single-crystalline graphene free of multilayer domains via a facile one-step delamination of epitaxial graphene from silicon carbide (SiC). We find that this is enabled by a specific surface reconstruction of 4H-SiC(0001) that we achieve under our growth conditions. The high crystalline quality of graphene after delamination and transfer from the SiC substrate is confirmed by the observation of key fingerprints of Dirac fermions in quantum transport: ambipolar charge transport, Shubnikov–de Haas oscillations up to filling factor ν=4N+2=74, with N the Landau index, Berry phase of π, and half-integer quantum Hall effect in cm-sized crystals. The scalability of our process, explored with recycled 4”-SiC wafers, represents an advance toward large-scale integration of high-performance graphene applications.

Magnesium (Mg) is an abundant metal which has been used in aviation, medicine, hydrogen energy storage, etc. However, Mg can be rather reactive, and therefore an improved understanding of corrosion and oxidation mechanisms can enhance the efficiency of these processes to control and widen applications. The study presented here investigates the mechanisms of oxidation from the initial to full monolayer stages, on two low-index Mg surfaces, Mg(0001) and Mg(1010). By analysing the valence electron changes during the oxidation process, we reveal a connection between oxidation and electron properties, suggesting that oxygen (O) atoms preferentially adsorb in the regions of charge accumulation on the surfaces. After the adsorption of a first O atom, the charge distribution on the surface changes, and following O atoms are attracted to neighbouring charge-rich regions. In addition, the oxidized Mg-O units form geometric structures initially different from the rocksalt structure commonly reported for a fully oxidized surface. In Mg(0001), the Mg-O unit structure transitions from a wurtzite type to hexagonal, while on Mg(1010) a more perfect Mg-O unit of wurtzite structure forms.

We introduce and illustrate use of two closely related range-separated hybrid (RSH) van der Waals density functionals (vdW-DFs), denoted AHBR-mRSH and AHBR-mRSH*, for total-energy and quasiparticle characterizations of molecules using generalized Kohn-Sham (gKS) density functional theory (DFT). For comparison, we also introduce and document a traditional design for a long-range corrected (LRC) vdW-DF, denoted 'B86R-LRC'. All three new vdW-DFs set the exchange potential as free of asymptotic screening in the coupling between the electron and its associated exchange hole. Our two AHBR-mRSHs are key members of a broader class 'AHBR-mRSH(γ)' defined by an inverse length scaleγfor a crossover in weighting short- and long-ranged exchange contributions; we obtain a highly accurate predictor of general molecular-energy differences by keepingγ = 0.106 (inverse Bohr) deliberately fixed in AHBR-mRSH. We obtain an optimally tuned (OT) form AHBR-mRSH* = AHBR-mRSH(γ∗) by computing a plausible value ofγ∗for specific types of systems. This AHBR-mRSH* permits characterizations of molecular quasiparticles and generalizes (1) the existing 'OT-RSH' (Steinet al2010Phys. Rev. Lett.105266802; Rafaely-Abramsonet al2012Phys. Rev. Lett.109226405) approach by a systematic inclusion of truly nonlocal correlations, and (2) more traditional LRC forms (e.g. B86R-LRC) by setting the short-range exchange description as in vdW-DF2-ahbr (Shuklaet al2022Phys. Rev. X12041003).Importantly,we may view AHBR-mRSH and AHBR-mRSH* as internally consistent functionals for gKS-DFT, being simultaneously accurate on molecular energies and quasiparticles. This is possible because the 'AHBR-mRSH(γ)' class has enough transferability to almost always limit adverse impacts of tuningγ, as tested here on the GMTKN55 benchmark suite (Goerigket al2017Phys. Chem. Chem. Phys.1932184). We find that AHBR-mRSH generally outperforms B86R-LRC on molecular problems. To illustrate usage, we complete the OT design of an AHBR-mRSH* for nucleobases and show that it provides quasiparticle predictions that are in good agreement with both literature theory and experimental values for adenine, thymine, cytosine, and guanine.

Producing large-area single-crystalline graphene is key to realizing its full potential in advanced applications, including twistronics. Yet, controlling graphene growth kinetics to avoid grain boundaries or multilayer growth remains challenging. Here, we demonstrate single-crystalline graphene free from multilayer domains via one-step delamination of epitaxial graphene from silicon carbide (SiC). This is enabled by a specific surface reconstruction of 4H-SiC(0001) achieved in our growth conditions. High crystalline quality is confirmed by the observation of the half-integer quantum Hall effect – the hallmark of monolayer graphene – in near cm-sized crystals. The scalability of our process, explored with 4”-wafers, represents an advance toward large-scale integration of high-performance graphene applications.

Weak bonding among bacteria phospholipids and less repulsive force when graphene materials approach, result in graphene materials interacting differently with the bacteria compared to mammalian cells.

In x-ray photoelectron spectroscopy (XPS), identifying the origin of peaks in the spectrum can be guided by theory calculations. With density functional theory (DFT), using pseudopotentials, one can obtain the difference in photoelectron energy for electrons originating from atoms of different environments, for example surface and bulk atoms, and thus model the surface core level shift (SCLS) energies. The focus in this work is to prepare for calculations of magnesium (Mg) 2p SCLSs in material systems where dispersion interactions play a role, primarily in Mg surface degradation and adsorption of molecules as relevant, for example, in degradable bioimplants. For SCLS DFT calculations in metallic surfaces, the state of the photoelectron must be treated as a core state. In the case of Mg, standard pseudopotentials treat the 2p state as a valence state, not a core state. We therefore need Mg pseudopotentials with the 2p electrons in the core, leaving only two electrons for the valence region (the 3s electron); Two-valence electron pseudopotentials are not common, because DFT calculations of Mg-containing materials usually are better or more easily described using 10 valence electrons. In this work, new two-electron Mg pseudopotentials are therefore created for use in dispersion-inclusive DFT calculations. To our knowledge, no such two-electron Mg pseudopotentials exist, proven to work well with the nonlocal, dispersion-inclusive, exchange-correlation functional vdW-DF-cx or similar functionals. We create a number of two-electron Mg pseudopotentials and their 2p-hole partners, and for four of the most promising we assess their performance in vdW-DF-cx. We provide results for Mg and MgO bulk phases and for the Mg(0001) surface energy, structure, and SCLS, and where possible we compare with results that we obtain by using conventional 10-electron Mg pseudopotentials, all-electron calculations, and with experiments. This work not only reports and tests the specific conditions for creating 2p Mg results, it will also, we believe, be of help in creating other similar pseudopotentials to aid the analysis of XPS spectra in other materials.

Magnesium (Mg) is a metal having a high structural efficiency and a very high chemical reactivity at the same time. Its potential areas of applications include the automotive industry, biomedicine, and energy storage and generation. Further developments in these very diverse application areas require a more detailed investigation of the behavior of Mg surfaces under oxidative conditions. The basic mechanisms of magnesium reactivity are not yet fully understood and therefore need to be further investigated by a combination of theoretical and experimental studies on representative surfaces with different crystallographic orientations.For this, we measured in situ high-resolution Mg 2p core level spectra at critical low-index Mg(0001), Mg (101¯0), and Mg (112¯0) surfaces to obtain surface core level shifts (SCLSs) at the early stages of Mg oxidation. We also used density functional theory (DFT) to obtain theoretical estimates of the SCLSs for respective surfaces and associated possible reconstructions to guide the analysis of the experimental spectra and to rule out un-reconstructed Mg (112¯0). DFT simulations were also used to reveal the energies of O atom adsorption, and the formation of evolving oxide structures in the Mg surfaces.

We introduce a new, general-purpose, range-separated hybrid van der Waals density functional termed vdW-DF2-ahbr within the nonempirical vdW-DF method [Hyldgaard, et al. J. Phys. Condens. Matter 32, 393001 (2020)]. It combines a correlation from vdW-DF2 with a screened Fock exchange that is fixed by a new model of exchange effects in the density-explicit vdW-DF-b86r or rev-vdW-DF2 functional [Hamada, Phys. Rev. B 89, 121103(R) (2014)]. The new vdW-DF2-ahbr prevents spurious exchange binding and has a small-density-gradient form set from many-body perturbation analysis. It is accurate for bulk as well as layered materials, and it systematically and significantly improves the performance of the present vdW-DFs for molecular problems. Importantly, vdW-DF2-ahbr also outperforms present-standard (dispersion-corrected) range-separated hybrids on a broad collection of noncovalent-interaction benchmark sets, while at the same time successfully mitigating the density-driven errors that often affect the description of molecular transition states and isomerization calculations. vdW-DF2-ahbr furthermore improves on state-of-the-art density-functional-theory approaches by succeeding at challenging problems. For example, it (1) correctly predicts both the substrate structure and the site preference for CO adsorption on Pt(111), (2) it outperforms existing nonempirical vdW-DFs for the description of CO2 adsorption in both a functionalized and in a simple metal-organic framework, and (3) it is highly accurate for the set of base-pair interactions in a model of DNA assembly.

We present the idea and illustrate potential benefits of having a tool chain of closely related regular, unscreened and screened hybrid exchange–correlation (XC) functionals, all within the consistent formulation of the van der Waals density functional (vdW-DF) method (Hyldgaard et al (2020 J. Phys.: Condens. Matter 32 393001)). Use of this chain of nonempirical XC functionals allows us to map when the inclusion of truly nonlocal exchange and of truly nonlocal correlation is important. Here we begin the mapping by addressing hard and soft material challenges: magnetic elements, perovskites, and biomolecular problems. We also predict the structure and polarization for a ferroelectric polymer. To facilitate this work and future broader explorations, we present a stress formulation for spin vdW-DF and illustrate the use of a simple stability-modeling scheme. The modeling supplements density functional theory (DFT) (with a specific XC functional) by asserting whether the finding of a soft mode (an imaginary-frequency vibrational mode, ubiquitous in perovskites and soft matter) implies an actual DFT-based prediction of a low-temperature transformation.

We need clean drinking water, but current water purification methods are not always sufficient. This study examines the binding and binding mechanisms when graphene oxide is used as a filter material for removing perfluorinated substances and trihalomethanes. We use density functional theory calculations to examine the binding of the harmful molecules on graphene oxide. Our results indicate that the binding energies between graphene oxide and the investigated molecules are in the range of 370-1450 meV per molecule, similar to the binding energies obtained in other studies, where adsorption of similar size molecules onto graphene oxide has been investigated. This indicates that graphene oxide has the potential to separate the molecules of interest from the water. Significant contribution to the binding energies comes from the van der Waals (dispersion) interaction between the molecule and graphene oxide, while the hydrogen bonding between the functional groups of graphene oxide and the hydrogen atoms in functional groups on the molecules also plays a role in the binding.

Riccardo Arpaia, 2, ∗ Eric Andersson, Alexei Kalaboukhov, Elsebeth Schröder, Edoardo Trabaldo, Regina Ciancio, Goran Dražić, Pasquale Orgiani, Thilo Bauch, and Floriana Lombardi † Quantum Device Physics Laboratory, Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-41296 Göteborg, Sweden Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133 Milano, Italy CNR-IOM, TASC Laboratory, Area Science Park, Basovizza S.S. 14 km 163.5, I-34149 Trieste, Italy Laboratory for Materials Chemistry, National Institute of Chemistry, Hajdrihova 19, SI-1001 Ljubljana, Slovenia CNR-SPIN, University of Salerno, I-84084 Fisciano (SA), Italy (Dated: August 8, 2019)

We have grown untwinned YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO) films on (110) MgO substrates that were pre-annealed at high temperature in oxygen atmosphere. The annealing results in surface reconstruction with shallow facets, which induce the suppression of the YBCO twinning domains, and the preferential alignment of the CuO chains along one of the in-plane directions of the sample. Because of the large mismatch between the in-plane lattice parameters of film and substrate, the strain induced by the MgO into the YBCO layer is strong and very peculiar. The YBCO film is compressed, with respect to the bulk, and presents a unidirectional buckling of the atomic planes, along the chains' direction, due to a deformation of the copper-oxygen octahedra. The YBCO films, which can be grown with thicknesses down to few unit cells and oxygen doping levels spanning most of the superconducting dome, are patterned into nanowires with dimensions down to 50 nm. The anisotropies due to the untwinning state are preserved in these structures; moreover, additional anisotropies appear, in ultrathin structures where strain effects become more pronounced. Such untwinned and compressively strained films can therefore be used as a platform to study the interplay between strain and the various local orders in the normal state of YBCO.

We study the phase stability and martensitic transformation of orthorhombic and monoclimic polyethylene by means of density functional theory using the nonempirical consistent-exchange vdW-DF-cx functional [Phys. Rev. B 89, 035412 (2014)]. The results show that the orthorhombic phase is the most stable of the two. Owing to the occurrence of soft librational phonon modes, the monoclimic phase is predicted not to be stable at zero pressure and temperature, but becomes stable when subjected to compressive transverse deformations that pin the chains and prevent them from wiggling freely. This theoretical characterization, or prediction, is consistent with the fact that the monoclimic phase is only observed experimentally when the material is subjected to mechanical loading. Also, the estimated threshold energy for the combination of lattice deformation associated with the T1 and T2 transformation paths (between the orthorhombic and monoclimic phases) and chain shuffling is found to be sufficiently low for thermally activated back transformations to occur. Thus, our prediction is that the crystalline part can transform back from the monoclimc to the orthorhombic phase upon unloading and/or annealing, which is consistent with experimental observations. Finally, we observe how a combination of such phase transformations can lead to a fold-plane reorientation from {110} to {100} type in a single orthorhombic crystal.