557 research outputs found
Density-density functionals and effective potentials in many-body electronic structure calculations
We demonstrate the existence of different density-density functionals
designed to retain selected properties of the many-body ground state in a
non-interacting solution starting from the standard density functional theory
ground state. We focus on diffusion quantum Monte Carlo applications that
require trial wave functions with optimal Fermion nodes. The theory is
extensible and can be used to understand current practices in several
electronic structure methods within a generalized density functional framework.
The theory justifies and stimulates the search of optimal empirical density
functionals and effective potentials for accurate calculations of the
properties of real materials, but also cautions on the limits of their
applicability. The concepts are tested and validated with a near-analytic
model.Comment: five figure
Exact-exchange density-functional theory for quasi-two-dimensional electron gases
A simple exact-exchange density-functional method for a quasi-two-dimensional
electron gas with variable density is presented. An analytical expression for
the exact-exchange potential with only one occupied subband is provided,
without approximations. When more subbands are occupied the exact-exchange
potential is obtained numerically. The theory shows that, in contradiction with
LDA, the exact-exchange potential exhibits discontinuities and the system
suffers a zero-temperature first-order transition each time a subband is
occupied. Results suggesting that the translational symmetry might be
spontaneously broken at zero temperature are presented. An extension of the
theory to finite temperatures allows to describe a drop in the intersubband
spacing in good quantitative agreement with recent experiments.Comment: 14 pages, 3 figure
Simple Impurity Embedded in a Spherical Jellium: Approximations of Density Functional Theory compared to Quantum Monte Carlo Benchmarks
We study the electronic structure of a spherical jellium in the presence of a
central Gaussian impurity. We test how well the resulting inhomogeneity effects
beyond spherical jellium are reproduced by several approximations of density
functional theory (DFT). Four rungs of Perdew's ladder of DFT functionals,
namely local density approximation (LDA), generalized gradient approximation
(GGA), meta-GGA and orbital-dependent hybrid functionals are compared against
our quantum Monte Carlo (QMC) benchmarks. We identify several distinct
transitions in the ground state of the system as the electronic occupation
changes between delocalized and localized states. We examine the parameter
space of realistic densities () and moderate depths of the
Gaussian impurity (). The selected 18 electron system (with closed-shell
ground state) presents transitions while the 30 electron system
(with open-shell ground state) exhibits transitions. For the former
system, the accuracy for the transitions is clearly improving with increasing
sophistication of functionals with meta-GGA and hybrid functionals having only
small deviations from QMC. However, for the latter system, we find much larger
differences for the underlying transitions between our pool of DFT functionals
and QMC. We attribute this failure to treatment of the exact exchange within
these functionals. Additionally, we amplify the inhomogeneity effects by
creating the system with spherical shell which leads to even larger errors in
DFT approximations.Comment: 8 pages, 4 figures, submitted to PRB as a regular article revisited
version after revie
Cyclobuteno[60]fullerenes as efficient n-type organic semiconductors
Cyclobuteno[3,4:1,2][60]fullerenes have been prepared in a straightforward manner by a simple reaction between [60]fullerene and readily available allenoates or alkynoates as organic reagents under basic and mild conditions. The chemical structure of the new modified fullerenes has been determined by standard spectroscopic techniques and confirmed by X-Ray diffraction analysis. Some of these new fullerene derivatives exhibit a remarkable intrinsic electron mobility â determined by using flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurements â which surpasses that of the well-known PCBM, thus behavi ng as promising n-type organic semiconductors
Transcriptomic effects of Tet-on and mifepristone-inducible systems in mouse liver
Control of transgene expression from long-term expression vectors can be achieved with inducible and regulated promoters. The two most commonly used inducible systems employ doxycycline or mifepristone as the drug activating a silent trans-activator, which is expressed from a constitutive promoter. We evaluated the alterations provoked by constitutive expression in the liver of rtTA2(S)-M2 (rtTA2; second-generation reverse tetracycline-controlled trans-activator) and GLp65, which are the trans-activators of the doxycyline- and mifepristone-inducible systems, respectively. To this end we performed transcriptomic analysis of mice expressing these trans-activators in the liver over 1 month. rtTA2 expression induced alterations in a few genes (69 gene probesets; false discovery rate [FDR], approximately 0.05), whereas GLp65 caused more numerous changes (1059 gene probe-sets, an FDR of approximately 0.05). However, only 20 and 53 of the genes from the rtTA2 and GLp65 groups, respectively, showed changes (R-fold >or= 3). Functional assignments indicate that alterations were mild and of little general significance. Few additional transcriptomic changes were observed when expressing trans-activators in the presence of inducer drugs; most were due to the drugs themselves. These results and the absence of toxicity observed in treated animals indicate that the two inducible systems are well tolerated and have little impact on the liver transcriptome profile. The milder alterations found with the use of rtTA2 suggest that this system is possibly safer for gene therapy application
Transcriptomic effects of Tet-on and mifepristone-inducible systems in mouse liver
Control of transgene expression from long-term expression vectors can be achieved with inducible and regulated promoters. The two most commonly used inducible systems employ doxycycline or mifepristone as the drug activating a silent trans-activator, which is expressed from a constitutive promoter. We evaluated the alterations provoked by constitutive expression in the liver of rtTA2(S)-M2 (rtTA2; second-generation reverse tetracycline-controlled trans-activator) and GLp65, which are the trans-activators of the doxycyline- and mifepristone-inducible systems, respectively. To this end we performed transcriptomic analysis of mice expressing these trans-activators in the liver over 1 month. rtTA2 expression induced alterations in a few genes (69 gene probesets; false discovery rate [FDR], approximately 0.05), whereas GLp65 caused more numerous changes (1059 gene probe-sets, an FDR of approximately 0.05). However, only 20 and 53 of the genes from the rtTA2 and GLp65 groups, respectively, showed changes (R-fold >or= 3). Functional assignments indicate that alterations were mild and of little general significance. Few additional transcriptomic changes were observed when expressing trans-activators in the presence of inducer drugs; most were due to the drugs themselves. These results and the absence of toxicity observed in treated animals indicate that the two inducible systems are well tolerated and have little impact on the liver transcriptome profile. The milder alterations found with the use of rtTA2 suggest that this system is possibly safer for gene therapy application
Locality Error Free Effective Core Potentials for 3d Transition Metal Elements Developed for the Diffusion Monte Carlo Method
Pseudopotential locality errors have hampered the applications of the
diffusion Monte Carlo (DMC) method in materials containing transition metals,
in particular oxides. We have developed locality error free effective core
potentials, pseudo-Hamiltonians, for transition metals ranging from Cr to Zn.
We have modified a procedure published by some of us in [M.C. Bennett et al,
JCTC 18 (2022)]. We carefully optimized our pseudo-Hamiltonians and achieved
transferability errors comparable to the best semilocal pseudopotentials used
with DMC but without incurring in locality errors. Our pseudo-Hamiltonian set
(named OPH23) bears the potential to significantly improve the accuracy of
many-body-first-principles calculations in fundamental science research of
complex materials involving transition metals
Elemental Composition of Commercial Herbal Tea Plants and Respective Infusions
Funding Information: Funding: This work received funding support from national funds from Fundação para a CiĂȘncia e a Tecnologia, I.P. (FCT), Portugal, through the research units UIDB/04035/2020 (GeoBioTec) and UIDB/00239/2020 (CEF). Publisher Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland.This study evaluated the elemental composition of 25 herbal tea plants commonly used in infusions by Portuguese consumers and the contribution to the elemental daily intake of some essential elements. Hydrocotyle asiatica (L.), Matricaria chamomilla (L.), and Melissa officinalis (L.) samples are a rich source of K with around 6.0 mg gâ1 while the Asteraceae Silybum marianum (L.) and Echinacea angustifolia (DC.) exhibited 4.9 and 5.6 mg gâ1 Ca, respectively. The highest concentrations of S and Zn were noted in Hydrocotyle asiatica (L.), while the highest concentration of Sr was found in Cassia angustifolia (Vahl.). In general, a large variability in the concentrations among different families and plant organs had been observed, except Cu with levels around 30 ”g gâ1. The principal component analysis (PCA) showed positive correlations between Zn and S and Sr and Ca, also revealing that Hydrocotyle asiatica (L.), Echinacea angustifolia (DC.), Silybum marianum (L.), and Cassia angustifolia (Vahl.) samples, stands out about all other samples regarding the enrichment of macro and micronutrients. The elemental solubility of macronutrients in the infusion is greater than the micronutrient solubility, despite the contribution to the recommended daily intake was weak. As a whole, Cynara scolymus (L.) and Hibiscus sabdariffa (L.) are the species with the best elemental solubilities, followed by Hydrocotyle asiatica (L.). No harmful elements, such as As and Pb, were observed in both the raw material and the infusions.publishersversionpublishe
Elemental Composition of Commercial Herbal Tea Plants and Respective Infusions
This study evaluated the elemental composition of 25 herbal tea plants commonly used
in infusions by Portuguese consumers and the contribution to the elemental daily intake of some
essential elements. Hydrocotyle asiatica (L.), Matricaria chamomilla (L.), and Melissa officinalis (L.)
samples are a rich source of K with around 6.0 mg g-1 while the Asteraceae Silybum marianum
(L.) and Echinacea angustifolia (DC.) exhibited 4.9 and 5.6 mg g-1 Ca, respectively. The highest
concentrations of S and Zn were noted in Hydrocotyle asiatica (L.), while the highest concentration of
Sr was found in Cassia angustifolia (Vahl.). In general, a large variability in the concentrations among
different families and plant organs had been observed, except Cu with levels around 30 g g-1. The
principal component analysis (PCA) showed positive correlations between Zn and S and Sr and Ca,
also revealing that Hydrocotyle asiatica (L.), Echinacea angustifolia (DC.), Silybum marianum (L.), and
Cassia angustifolia (Vahl.) samples, stands out about all other samples regarding the enrichment of
macro and micronutrients. The elemental solubility of macronutrients in the infusion is greater than
the micronutrient solubility, despite the contribution to the recommended daily intake was weak.
As a whole, Cynara scolymus (L.) and Hibiscus sabdariffa (L.) are the species with the best elemental
solubilities, followed by Hydrocotyle asiatica (L.). No harmful elements, such as As and Pb, were
observed in both the raw material and the infusionsinfo:eu-repo/semantics/publishedVersio
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