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At supercooled temperatures, liquid fluidity requires barrier crossing on the multidimensional potential energy surface or landscape. However, most equilibrium quantities are then dominated by configurations close to the local minima and do not contain information about the barriers. Thus, they are not indicated as the basis of a theory for long-time dynamics, specifically, for the self-diffusion constant, D (T). By contrast, the unstable instantaneous normal modes (INMs) are well-defined equilibrium properties with contributions only from configurations with some downward curvature of the potential, primarily, regions above the inflection points and the barriers. They are uniquely well suited to describe long-time dynamics, and the results of pursuing that idea are described herein: (1) The well developed and successful INM theory of self-diffusion. (2) The theory and functional form of the unstable density of states, which contains information about the topography of the landscape, a significant factor in the nature of supercooled dynamics. (3) A random energy model and the soft potential model provide simplification and add additional insight. (4) Despite the focus on dynamics, the configurational entropy is expressed in terms of the unstable INM, and the heat capacity has unstable INM contributions. [ABSTRACT FROM AUTHOR]

The Ryabinkin–Kohut–Staroverov (RKS) and Kanungo–Zimmerman–Gavini (KZG) methods offer two approaches to find exchange-correlation (XC) potentials from ground state densities. The RKS method utilizes the one- and two-particle reduced density matrices to alleviate any numerical artifacts stemming from a finite basis (e.g., Gaussian- or Slater-type orbitals). The KZG approach relies solely on the density to find the XC potential by combining a systematically convergent finite-element basis with appropriate asymptotic correction on the target density. The RKS method, being designed for a finite basis, offers computational efficiency. The KZG method, using a complete basis, provides higher accuracy. In this work, we combine both methods to simultaneously afford accuracy and efficiency. In particular, we use the RKS solution as an initial guess for the KZG method to attain a significant 3–11× speedup. This work also presents a direct comparison of the XC potentials from the RKS and the KZG method and their relative accuracy on various weakly and strongly correlated molecules, using their ground state solutions from accurate configuration interaction calculations solved in a Slater orbital basis. [ABSTRACT FROM AUTHOR]

Second-order Møller–Plesset perturbation theory is well-known as a computationally inexpensive approach to the electron correlation problem that is size-consistent with a size-consistent reference but fails to be regular. On the other hand, the less well-known many-body version of Brillouin–Wigner perturbation theory has the reverse properties: it is regular but fails to be size-consistent when used with the standard MP partitioning. Consequently, its widespread use remains limited. In this work, we analyze the ways in which it is possible to use alternative non-MP partitions of the Hamiltonian to yield variants of BW2 that are size-consistent as well as regular. We show that there is a vast space of such BW2 theories and also show that it is possible to define a repartitioned BW2 theory from the ground state density alone, which regenerates the exact correlation energy. We also provide a general recipe for deriving regular, size-consistent, and size-extensive partitions from physically meaningful components, and we apply the result to small model systems. The scope of these results appears to further set the stage for a revival of BW2 in quantum chemistry. [ABSTRACT FROM AUTHOR]

The quantum-electrodynamic non-adiabatic emission (QED-NAE) is a type of radiatively assisted vibronic de-excitation due to electromagnetic vacuum fluctuations on non-adiabatic processes. Building on our previous work [Tsai et al., J. Phys. Chem. Lett. 14, 5924 (2023)], we extend the theory of the QED-NAE rate from a single cavity photonic mode to infinite photonic modes and calculate the QED-NAE rates of 9-cyanoanthracene at the first-principles level. To avoid the confusion, the quantum electrodynamic internal conversion process is renamed as "QED-NAE" in our present work. According to our theory, we identify three key factors influencing the QED-NAE processes: light–matter coupling strength (mode volume), mass-weighted orientation factor, and photonic density of states. The mode volume is the primary factor causing rate differences between the two scenarios. In a single cavity with a small mode volume, strong light–matter coupling strength boosts QED-NAE rates. In contrast, in free space with infinite photonic modes, weak coupling strength significantly reduces these rates. From a single cavity photonic mode to infinite photonic modes, the mass-weighted orientation factor only causes an 8π/3-fold increase in the QED-NAE rate. In free space, the photonic density of state exhibits a flat and quadratic distribution, which slightly reduces the QED-NAE rate. Our study shows that cavities can significantly enhance non-adiabatic QED effects while providing a robust analysis demonstrating that QED vibronic effects can be safely ignored in free space. [ABSTRACT FROM AUTHOR]

It is now established that glasses feature low-frequency, nonphononic excitations, in addition to phonons that follow Debye's vibrational density of state (VDoS). Extensive computer studies demonstrated that these nonphononic, glassy excitations follow a universal non-Debye VDoS D G (ω) ∼ ω 4 at low frequencies ω. Yet, due to intrinsic difficulties in disentangling D G (ω) from the total VDoS D (ω) , which is experimentally accessible through various scattering techniques, the ω 4 tail of D G (ω) lacked direct experimental support. We develop a procedure to extract D G (ω) from the measured D (ω) , based on recent advances in understanding low-frequency excitations in glasses, and apply it to available datasets for diverse glasses. The resulting analysis indicates that the ω 4 tail of the nonphononic vibrational spectra of glasses is nontrivially consistent with a broad range of experimental observations. It also further supports that D G (ω) makes an additive contribution to D (ω). [ABSTRACT FROM AUTHOR]

The temperature and drain current (ID) dependencies of sub-threshold swing (SS) values of Si n- and p-channel metal–oxide–semiconductor field effect transistors (MOSFETs) with different substrate impurity concentrations ranging from the 1015 to 1018 cm−3 ranges are systematically and experimentally evaluated at cryogenic temperatures. It is found that SS of p-channel MOSFETs tends to increase with decreasing temperature, which contrasts with saturation of SS of n-MOSFETs at cryogenic temperatures, well reported by many previous works. To explain these SS behaviors quantitatively, we employ a density-of-state (DOS) model with tail states consisting of localized states in a deep energy range and mobile states in a shallow energy range, which are attributable to potential fluctuations caused by substrate impurities. It is shown that this model can quantitatively explain the temperature and ID dependencies of SS of both n-MOSFETs and p-MOSFETs. Then, we are assuming that the Si p-MOSFET has a higher density of localized states than the n-MOSFET. Thus, the increase in SS of the p-MOSFETs with decreasing temperature is explained by an increase in the density of localized states at the Fermi level with decreasing temperature, because the density of localized states increases with elevating the Fermi level position in the employed DOS model. [ABSTRACT FROM AUTHOR]

Thermal rectification (TR) has attracted significant research interest due to its potential to achieve active heat control in various nanoscale applications. In this study, we propose a novel graphene-based thermal rectifier under a strain gradient. Two kinds of strain gradients, namely, compressive and tensile, are considered. We observe that under a compressive strain gradient (CSGG), the heat flows preferentially from the high-compressed region to the lower, with a significant TR of 120%. But for a tensile strain gradient (TSGG), the direction of TR is dependent on its length. For a smaller system, the TR occurs from the high-strained to low-strained region, while for larger systems, the direction of TR is reversed. The strength and location of the standing wave in conjunction with the mismatch in the overlap of the density of states in forward and reverse bias are found to induce TR in TSGG and CSGG. The TR direction is observed to be altered by changing the location of the strain gradient. Additionally, we propose a series thermal rectifier by coupling graphene under strain gradient to asymmetric defective graphene (ADG). A significant increase in the series thermal rectifier is observed when compared to TR in ADG. Our results demonstrate the applicability of strain gradient as a feasible approach to control the thermal rectification ratio and its direction for various applications such as phononic devices and thermal logic circuits. [ABSTRACT FROM AUTHOR]

This study investigates the compound system Mn5−xZnxGe3 (x = 0.1, 0.2, and 0.3) through experimental investigations and theoretical calculations. Zn doping lowers the Curie temperature and magnetic entropy change of Mn5−xZnxGe3 alloys. Analysis of phenomenological curves, including Landau theories, normalized curves, and Arrott curves during the study of isothermal magnetization curves, reveals a second-order phase transition in this system. Through an extensive investigation of critical behavior using critical isotherm curves and the Kouvel–Fisher (KF) method, the consistency and reliability of these critical indices are validated by the prediction of the scaling theory in the critical region. By scaling the dependence of |ΔSM| on M and applying crucial exponen21t values, an efficient new approach is utilized to calculate the spontaneous magnetization that agrees well with the values deduced from the KF method. Additionally, first-principles calculations reveal that the Mn atoms' 3d orbitals are more significantly close to the Fermi energy level, with Zn doping generally reducing both the electronic density of states and the total magnetic moment of the Mn 3d orbitals. Consequently, the introduction of Zn leads to a decrease in the Mn–Mn atom exchange coupling, resulting in a deterioration of the total exchange interaction. This phenomenon also explains the decrease in the Curie temperature TC due to Zn doping, aligning with experimental observations. [ABSTRACT FROM AUTHOR]

We present a theoretical investigation of thermoelectric transport properties of bismuth-based ternary chalcogenides Pt3Bi4X9 (X = S, Se), which has low thermal conductivity and promising zT as discovered in a recent experiment [Wang et al., J. Am. Chem. Soc. 146, 7352 (2024)], using density functional theory combined with the Boltzmann transport equation within rigid band approximation. We find that the high density of states of valence bands near the Fermi level yields high p-type Seebeck coefficient. The lower effective mass of electron in Pt3Bi4S9 leads to high mobility and long relaxation time, and hence the high n-type electrical conductivity. In contrast, the effective mass of electron is much higher than that of hole in Pt3Bi4Se9 due to the flatted conduction band, which in turn gives rise to higher p-type electrical conductivity. As a result, the p-type zT is much higher than n-type in Pt3Bi4Se9, with an optimal value of 0.5 at 300 K. Considering the experimental carrier concentration for Pt3Bi4S9 (−1.4 × 1019 cm−3) and Pt3Bi4Se9 (−0.898 × 1019 cm−3), calculated n-type zT at 773 K are 0.52 and 0.04, respectively, which are consistent well with the experimental values. Our calculations uncover the upper limit thermoelectric zT of Pt3Bi4X9 and also highlight them as promising thermoelectric materials. [ABSTRACT FROM AUTHOR]

The doping influenced carrier dynamics to maneuvering n-type to p-type semiconducting gold cluster assembly have been assessed. The resonance photoemission spectroscopic measurements corroborate an incremental rise in the density of states at the valence edge, the overlap of valence states due to doping, and the presence of distinct spin–orbit splitting and coupling in manganese-doping (Au7Mn) compared to gold clusters (Au8), originating from the relativistic effect resulted in a semiconducting property. The work function dependent current–voltage characteristics in metal–semiconductor configuration show Ohmic and Schottky behaviors assorting p-type carriers in Au7Mn in contrast to the n-type Au8 and are presenting an atomic cluster based fast electronic device. [ABSTRACT FROM AUTHOR]

Refractory high-entropy alloys (RHEAs) have attracted increasing interest due to their excellent mechanical properties under extreme conditions. However, the lattice thermal conductivity is still not well studied. In this paper, we calculate the lattice thermal conductivity of the NbMoTaW RHEA using the equilibrium molecular dynamics method with a machine learning-based interatomic potential. We find that with increasing Mo concentration, the lattice thermal conductivity increased from 1.72 to 2.16 W/mK, an increase of 25.6%. The underlying mechanism is explained by the phonon density of states and phonon mode participation. Increasing the Mo concentration can induce a blueshift in both the low-frequency and high-frequency phonons. Moreover, we find that at the frequency corresponding to the phonon density of states peak, the NbMo1.5TaW RHEA has the largest mode participation rate, which is the main reason for the anomalous lattice thermal conductivity. In addition, we investigate the effect of temperature on the lattice thermal conductivity and the results show that anharmonicity has a dominant effect. Finally, the effect of compressive strain on the lattice thermal conductivity is explored. Our work discloses that the phonon density of states associated with phonon mode participation plays critical roles in the thermal conductivity of the RHEA, rather than the previously recognized conformational entropy. This contributes to the understanding of the thermal behavior of RHEA and provides an effective route to tune its thermal conductivity. [ABSTRACT FROM AUTHOR]