Development of an exchange–correlation functional with uncertainty quantification capabilities for density functional theory

This paper presents the development of a new exchange–correlation functional from the point of view of machine learning. Using atomization energies of solids and small molecules, we train a linear model for the exchange enhancement factor using a Bayesian approach which allows for the quantification of uncertainties in the predictions. A relevance vector machine is used to automatically select the most relevant terms of the model. We then test this model on atomization energies and also on bulk properties. The average model provides a mean absolute error of only 0.116 eV for the test points of the G2/97 set but a larger 0.314 eV for the test solids. In terms of bulk properties, the prediction for transition metals and monovalent semiconductors has a very low test error. However, as expected, predictions for types of materials not represented in the training set such as ionic solids show much larger errors

Study of Local Power Dissipation in Ultrascaled Silicon Nanowire FETs

The local electron power dissipation has been calculated in a field-effect nanowire transistor using a quantum transport formalism. Two different channel cross sections and optical and acoustic phonon mechanisms were considered. The phonon models used reproduce the phonon limited mobility in the cross sections studied. The power dissipation for different combinations of source, channel, and drain dimensions have been calculated. Due to the lack of complete electron energy relaxation inside the device, the Joule heat dissipation over-estimates the power dissipated in small nanotransistors. This over-estimation is larger for large cross sections due to the weaker phonon scattering. On the other hand, in narrow wires, the power dissipation inside the device can be large, therefore, mitigating against fabrication of very narrow nanowire transistors. We have also investigated the cooling of the device source region due to the mismatch of the Peltier coefficients between the source and the channel

Impact of phonon scattering in Si/GaAs/InGaAs nanowires and FinFets: a NEGF perspective

This paper reviews our previous theoretical studies and gives further insight into phonon scattering in 3D small nanotransistors using non-equilibrium Green function methodology. The focus is on very small gate-all-around nanowires with Si, GaAs or InGaAs cores. We have calculated phonon-limited mobility and transfer characteristics for a variety of cross-sections at low and high drain bias. The nanowire cross-sectional area is shown to have a significant impact on the phonon-limited mobility and on the current reduction. In a study of narrow Si nanowires we have examined the spatially resolved power dissipation and the validity of Joule’s law. Our results show that only a fraction of the power is dissipated inside the drain region even for a relatively large simulated length extension (approximately 30 nm). When considering large source regions in the simulation domain, at low gate bias, a slight cooling of the source is observed. We have also studied the impact of the real part of phonon scattering self-energy on a narrow nanowire transistor. This real part is usually neglected in nanotransistor simulation, whereas we compute its impact on current–voltage characteristic and mobility. At low gate bias, the imaginary part strongly underestimated the current and the mobility by 50 %. At high gate bias, the two mobilities are similar and the effect on the current is negligible

Spin-polarized transport in a full magnetic pn tunnel junction

Simulations of the tunneling current as a function of voltage and temperature for a Zener diode where both sides are ferromagnetic have been performed. The current is evaluated as a function of the applied bias, the magnetization, and the temperature on the diode. The tunneling magnetoresistance is also analyzed. Mn doped GaAs parameters were used to simulate a highly asymmetric doped diode, which leads to a large difference on the magnetization values between the p and n sidesThis work was supported by Spanish Government Grant Nos. TIN2007-67537-C03-01 and TEC2010-17320 and by Xunta de Galicia Grant Nos. DXIDI09TIC001CT and INCITE08PXIB206094PRS

Comparison of fin-edge roughness and metal grain work function variability in InGaAs and Si FinFETs

The fin-edge roughness (FER) and the TiN metal grain work function (MGW)-induced variability affecting OFF and ON device characteristics are studied and compared between a 10.4 nm gate length In0.53Ga0.47As FinFET and a 10.7 nm gate length Si FinFET. We have analyzed the impact of variability by assessing five figures of merit (threshold voltage, subthreshold slope, OFF-current, drain-induced-barrier-lowering, and ON-current) using the two state-of-the-art in-house-build 3-D simulation tools based on the finite-element method. Quantum-corrected 3-D drift-diffusion simulations are employed for variability studies in the subthreshold region while, in the ON-region, we use quantum-corrected 3-D ensemble Monte Carlo simulations. The In0.53Ga0.47As FinFET is more resilient to the FER and MGW variability in the subthreshold compared with the Si FinFET due to a stronger quantum carrier confinement present in the In0.53Ga0.47As channel. However, the ON-current variability is between 1.1 and 2.2 times larger for the In0.53Ga0.47As FinFET than for the Si counterpart, respectively

Anisotropic Quantum Corrections for 3-D Finite-Element Monte Carlo Simulations of Nanoscale Multigate Transistors

Anisotropic 2-D Schrödinger equation-based quantum corrections dependent on valley orientation are incorporated into a 3-D finite-element Monte Carlo simulation toolbox. The new toolbox is then applied to simulate nanoscale Si Siliconon-Insulator FinFETs with a gate length of 8.1 nm to study the contributions of conduction valleys to the drive current in various FinFET architectures and channel orientations. The 8.1 nm gate length FinFETs are studied for two cross sections: rectangular-like and triangular-like, and for two channel orientations: 〈100〉 and 〈110〉. We have found that quantum anisotropy effects play the strongest role in the triangular-like 〈100〉 channel device increasing the drain current by ~13% and slightly decreasing the current by 2% in the rectangular-like 〈100〉 channel device. The quantum anisotropy has a negligible effect in any device with the 〈110〉 channel orientation

Unraveling the periprandial changes in brain serotonergic activity and its correlation with food intake-related neuropeptides in rainbow trout Oncorhynchus mykiss

This study explored changes in brain serotonin content and activity together with hypothalamic neuropeptide mRNA abundance around feeding time in rainbow trout, as well as the effect of one-day fasting. Groups of trout fed at two (ZT2) and six (ZT6) hours after lights on were sampled from 90 minutes before to 240 minutes after feeding, while additional groups of non-fed trout were also included in the study. Changes in brain amine and metabolite contents were measured in hindbrain, diencephalon and telencephalon, while in the diencephalon the mRNA abundance of tryptophan hydroxylase ( tph1 , tph2 ), serotonin receptors (5htr1a , 5htr1b and 5htr2c ) and several neuropeptides ( npy , agrp1 , cartpt , pomca1 , crfb ) involved in the control of food intake were also assessed. The results showed changes in the hypothalamic neuropeptides that were consistent with the expected role for each in the regulation of food intake in rainbow trout. Serotonergic activity increased rapidly at the time of food intake in the diencephalon and hindbrain and remained high for much of the postprandial period. This increase in serotonin abundance was concomitant with elevated levels of pomca1 mRNA in the diencephalon, suggesting that serotonin might act on brain neuropeptides to promote a satiety profile. Furthermore, serotonin synthesis and neuronal activity appear to increase already before the time of feeding, suggesting additional functions for this amine before and during food intake. Exploration of serotonin receptors in the diencephalon revealed only small changes for gene expression of 5htr1b and 5htr2c receptors during the postprandial phase. Therefore, the results suggest that serotonin may play a relevant role in the regulation of feeding behavior in rainbow trout during periprandial time, but a better understanding of its interaction with brain centers involved in receiving and processing food-related signals is still needed.Agencia Estatal de Investigación | Ref. PID2022-136288OB-C31Xunta de Galicia | Ref. ED431B 2019/37Agencia Estatal de Investigación | Ref. BES-2017-079708Xunta de Galicia | Ref. ED481B-2022-08

Environmental and Health Benefits Assessment of Reducing PM2.5 Concentrations in Urban Areas in Developing Countries: Case Study Cartagena de Indias

High concentrations of particulate matter (PM) could significantly reduce the quality of useful life and human life expectancy. The origin, control, and management of the problem has made great steps in recent decades. However, the problem is still prominent in developing countries. In fact, often the number and spatial distribution of the air quality monitoring stations does not have an appropriate design, misleading decision makers. In the present research, an innovative assessment is proposed of the environmental, health and economic benefits corresponding to a 20% reduction in the PM2.5 concentration in the urban area of Cartagena de Indias, Colombia. Cases of mortality and morbidity attributable to fine particles (PM2.5) were estimated, with particular emphasis on mortality, emergency room visits and hospitalizations from respiratory diseases, in addition to their economic assessment using BenMAP-CE®. The novelty of using BenMAP-CE® in studying respiratory diseases and PM2.5 exposure in developing countries lies in its ability to provide a comprehensive assessment of the health impacts of air pollution in these regions. This approach can aid in the development of evidence-based policy and intervention strategies to mitigate the impact of air pollution on respiratory health. Several concentration-response (C-R) functions were implemented to find PM2.5 attributable mortality cases of ischemic heart and cardiopulmonary disease, lung cancer, respiratory and cardiovascular disease, as well as cases of morbidity episodes related to asthma exacerbation and emergency room/hospitalization care for respiratory disease. A 20% reduction would have avoided 104 cases of premature death among the population older than 30 in Cartagena, and around 65 cases of premature mortality without external causes

3-D Finite Element Monte Carlo Simulations of Scaled Si SOI FinFET With Different Cross Sections

Si SOI FinFETs with gate lengths of 12.8 nm and 10.7 nm are modelled using 3D Finite Element Monte Carlo (MC) simulations with 2D Schroedinger equation quantum corrections. These non-planar transistors are studied for two cross-sections: rectangular-like and triangular-like, and for two channel orientations: h100i and h110i. The 10.7 nm gate length rectangular-like FinFET is also simulated using the 3D Non-Equilibrium Green’s Functions (NEGF) technique and the results are compared with MC simulations. The 12.8 nm and 10.7 nm gate length rectangular-like FinFETs give larger drive currents per perimeter by about 25−27% than the triangular-like shaped but are outperformed by the triangular-like ones when normalised by channel area. The devices with a <100> channel orientation deliver a larger drive current by about 11% than their counterparts with a h110i channel when scaled to 12.8 nm and to 10.7 nm gate lengths. ID–VG characteristics at low and high drain biases obtained from the 3D NEGF simulations show a remarkable agreement with the MC results and overestimate the drain current from a gate bias of 0.5 V only due to exclusion of the interface roughness and ionized impurity scatterings

Novel synthesis of platinum complexes and their intracellular delivery to tumor cells by means of magnetic nanoparticles

Platinum-based drugs are popular in clinics as chemotherapeutic agents to treat solid tumors