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Myotonic dystrophy type I (DM1) is the most common form of adult muscular dystrophy and is a severe condition with no treatment currently available. Recently, small-molecule ligands have been developed as targeted covalent inhibitors that have some selectivity for and covalently inhibit cyclin-dependent kinase 12 (CDK12). CDK12 is involved in the transcription of elongated RNA sections that results in the DM1 condition. The covalent bond is achieved after nucleophilic addition to a Michael acceptor warhead. Previous studies of the conformational preferences of thio-Michael additions have focused on characterizing the reaction profile based on the distance between the sulfur and β-carbon atoms. Rotamerism, however, has not been investigated extensively. Here, we use high-level quantum chemistry calculations, up to coupled cluster with single, double, and perturbative triple excitations [CCSD(T)], to characterize the nucleophilic addition of an archetypal nucleophile, methanethiolate, to various nitrogen-containing Michael acceptors which are representative of the small-molecule covalent inhibitors. By investigating the structural, energetic, and electronic properties of the resulting enolates, as well as their reaction profiles, we show that synclinal additions are generally energetically favored over other additions due to the greater magnitude of attractive noncovalent interactions permitted by the conformation. The calculated transition states associated with the addition process indicate that synclinal addition proceeds via lower energetic barriers than antiperiplanar addition and is the preferred reaction pathway.

Two-dimensional (2D) magnetic crystals hold promise for miniaturized and ultralow power electronic devices that exploit spin manipulation. In these materials, large, controllable magnetocrystalline anisotropy (MCA) is a prerequisite for the stabilization and manipulation of long-range magnetic order. In known 2D magnetic crystals, relatively weak MCA typically results in soft ferromagnetism. Here, we demonstrate that ferromagnetic order persists down to the thinnest limit of FexTaS2(Fe-intercalated bilayer 2H-TaS2) with giant coercivities up to 3 T. We prepare Fe-intercalated TaS2by chemical intercalation of van der Waals-layered 2H-TaS2crystals and perform variable-temperature transport, transmission electron microscopy, and confocal Raman spectroscopy measurements to shed new light on the coupled effects of dimensionality, degree of intercalation, and intercalant order/disorder on the hard ferromagnetic behavior of FexTaS2. More generally, we show that chemical intercalation gives access to a rich synthetic parameter space for low-dimensional magnets, in which magnetic properties can be tailored by the choice of the host material and intercalant identity/amount, in addition to the manifold distinctive degrees of freedom available in atomically thin, van der Waals crystals.

Understanding growth mechanisms and the role of surface functionalization is of key importance to control shape and morphology of nanoparticles and their properties. Here, we describe the growth mechanism and the effect of hydrothermal synthesis parameters (pH, time, and precursor/functionalization agent ratio) during in situ functionalization of anatase TiO2nanoparticles with 3-aminopropyltriethoxysilane. Elongated crystallographically oriented TiO2nanoparticles were formed by oriented attachment mechanism in addition to spherical nanoparticles. The growth mechanism is determined by a combination of ex situ techniques such as high-resolution transmission electron microscopy combined with in situ synchrotron X-ray diffraction and density functional theory calculations. Oriented attachment induced by the functionalization agent is shown to be the origin of the elongation of the nanoparticles, as only spherical nanoparticles were formed in the absence of surface functionalization. Finally, it was shown that the amount and the size of the elongated nanoparticles can be tuned by adjusting pH.

The electronic structure of layered molybdenum trioxide MoO3is highly sensitive to changes in oxygen stoichiometry as Mo6+has an empty 4d shell. Applications of MoO3are responsive to small changes in vacancy concentration, with some functions relying on a narrow window of oxygen nonstoichiometry. Difficulties in analyzing the energetics of oxygen vacancies by computational methods stem from the inability to accurately model the layered structure of MoO3. One unit cell parameter is governed by long-range forces across the structural gaps, and these dispersed interactions are not well described by conventional density functional theory (DFT) methods. With the exchange functional vdW-DF2, we accurately model the structure, in good agreement with experimental data. This basis allows exploration of the effect of oxygen nonstoichiometry on the electronic structure and properties of the oxygen-deficient material. The layered structure efficiently screens the structural perturbations caused by oxygen vacancies. The enthalpies of formation are calculated for oxygen vacancies at the three symmetry inequivalent oxygen sites. The oxygen deficiency in MoO3gives rise to Mo 4d gap states with energy levels dependent on the type of oxygen vacancy.

Solid-state materials are currently being explored as a platform for the manipulation of spins for spintronics and quantum information science. More broadly, a wide spectrum of ferroelectric materials, spanning from inorganic oxides to polymeric systems such as PVDF, present a different approach to explore quantum phenomena in which the spins are set and manipulated with electric fields. Using dilute Fe3+-doped ferroelectric PbTiO3–SrTiO3superlattices as a model system, we demonstrate intrinsic spin–polarization control of spin directionality in complex ferroelectric vortices and skyrmions. Electron paramagnetic resonance (EPR) spectra show that the spins in the Fe3+ion are strongly coupled to the local polarization and preferentially aligned perpendicular to the ferroelectric polar caxis in this complex vortex structure. The effect of polarization–spin directionality is corroborated by first-principles calculations, demonstrating the variation of the spin directionality with the polar texture and offering the potential for future quantum analogues of macroscopic magnetoelectric devices.

Transition metal dichalcogenides (TMDs) offer superior properties over conventional materials in many areas such as in electronic devices. In recent years, TMDs have been shown to display a phase switching mechanism under the application of external mechanical strain, making them exciting candidates for phase change transistors. Molybdenum ditelluride (MoTe2) is one such material that has been engineered as a strain-based phase change transistor. In this work, we explore various aspects of the mechanical properties of this material by a suite of computational and experimental approaches. First, we present parameterization of an interatomic potential for modeling monolayer as well as multilayered MoTe2 films. For generating the empirical potential parameter set, we fit results from density functional theory calculations using a random search algorithm known as particle swarm optimization. The potential closely predicts structural properties, elastic constants, and vibrational frequencies of MoTe2 indicating a reliable fit. Our simulated mechanical response matches earlier larger scale experimental nanoindentation results with excellent prediction of fracture points. Simulation of uniaxial tensile deformation by molecular dynamics shows the complete non-linear stress-strain response up to failure. Mechanical behavior, including failure properties, exhibits directional anisotropy due to the variation of bond alignments with crystal orientation. Furthermore, we show the deterioration of mechanical properties with increasing temperature. Finally, we present computational and experimental evidence of an extended c-axis strain transfer length in MoTe2 compared to TMDs with smaller chalcogen atoms.

We extend the calculation of dark matter direct detection rates via electronic transitions in general dielectric crystal targets, combining state-of-the-art density functional theory calculations of electronic band structures and wave functions near the band gap, with semianalytic approximations to include additional states farther away from the band gap. We show, in particular, the importance of all-electron reconstruction for recovering large momentum components of electronic wave functions, which, together with the inclusion of additional states, has a significant impact on direct detection rates, especially for heavy mediator models and at O(10  eV) and higher energy depositions. Applying our framework to silicon and germanium (that have been established already as sensitive dark matter detectors), we find that our extended calculations can appreciably change the detection prospects. Our calculational framework is implemented in an open-source program exceed-dm (Extended Calculation of Electronic Excitations for Direct detection of Dark Matter), to be released in an upcoming publication. [ABSTRACT FROM AUTHOR]

Direct-detection experiments for light dark matter are making enormous leaps in reaching previously unexplored model space. Several recent proposals rely on collective excitations, where the experimental sensitivity is highly dependent on detailed properties of the target material, well beyond just nucleus mass numbers as in conventional searches. It is thus important to optimize the target choice when considering which experiment to build. We carry out a comparative study of target materials across several detection channels, focusing on electron transitions and single (acoustic or optical) phonon excitations in crystals, as well as the traditional nuclear recoils. We compare materials currently in use in nuclear recoil experiments (Si, Ge, NaI, CsI, CaWO4), a few of which have been proposed for light dark matter experiments (GaAs, Al2O3, diamond), as well as 16 other promising polar crystals across all detection channels. We find that target- and dark-matter-model-dependent reach is largely determined by a small number of material parameters: speed of sound, electronic band gap, mass number, Born effective charge, high-frequency dielectric constant, and optical phonon energies. We showcase, for each of the two benchmark models, an exemplary material that has a better reach than in any currently proposed experiment. [ABSTRACT FROM AUTHOR]

We propose the use of silicon carbide (SiC) for direct detection of sub-GeV dark matter. SiC has properties similar to both silicon and diamond but has two key advantages: (i) it is a polar semiconductor which allows sensitivity to a broader range of dark matter candidates; and (ii) it exists in many stable polymorphs with varying physical properties and hence has tunable sensitivity to various dark matter models. We show that SiC is an excellent target to search for electron, nuclear and phonon excitations from scattering of dark matter down to 10 keV in mass, as well as for absorption processes of dark matter down to 10 meV in mass. Combined with its widespread use as an alternative to silicon in other detector technologies and its availability compared to diamond, our results demonstrate that SiC holds much promise as a novel dark matter detector. [ABSTRACT FROM AUTHOR]