256 research outputs found
Prosocial nudges and visual indicators increase social distancing, but authoritative nudges do not.
Social distancing reduces the transmission of COVID-19 and other airborne diseases. To test different ways to increase social distancing, we conducted a field experiment at a major US airport using a system that presented color-coded visual indicators on crowdedness. We complemented those visual indicators with nudges commonly used to increase COVID-19-preventive behaviors. Analyzing data from 57,146 travelers, we find that visual indicators and nudges significantly affected social distancing. Introducing visual indicators increased the share of travelers practicing social distancing, and this positive effect was enhanced by introducing nudges focused on personal benefits ("protect yourself") and public benefits ("protect others"). Conversely, an authoritative nudge referencing the Centers for Disease Control and Prevention ("don't break CDC COVID-19 guidelines") did not change social distancing behavior. Our results demonstrate that visual indicators and informed nudges can boost social distancing and potentially curb the spread of contagious diseases
Ensemble v-representable ab-initio density functional calculation of energy and spin in atoms: atest of exchange-correlation approximations
The total energies and the spin states for atoms and their first ions with Z
= 1-86 are calculated within the the local spin-density approximation (LSDA)
and the generalized-gradient approximation (GGA) to the exchange-correlation
(xc) energy in density-functional theory. Atoms and ions for which the
ground-state density is not pure-state v-representable, are treated as ensemble
v- representable with fractional occupations of the Kohn-Sham system. A newly
developed algorithm which searches over ensemble v-representable densities [E.
Kraisler et al., Phys. Rev. A 80, 032115 (2009)] is employed in calculations.
It is found that for many atoms the ionization energies obtained with the GGA
are only modestly improved with respect to experimental data, as compared to
the LSDA. However, even in those groups of atoms where the improvement is
systematic, there remains a non-negligible difference with respect to the
experiment. The ab-initio electronic configuration in the Kohn-Sham reference
system does not always equal the configuration obtained from the spectroscopic
term within the independent-electron approximation. It was shown that use of
the latter configuration can prevent the energy-minimization process from
converging to the global minimum, e.g. in lanthanides. The spin values
calculated ab-initio fit the experiment for most atoms and are almost
unaffected by the choice of the xc-functional. Among the systems with
incorrectly obtained spin there exist some cases (e.g. V, Pt) for which the
result is found to be stable with respect to small variations in the
xc-approximation. These findings suggest a necessity for a significant
modification of the exchange-correlation functional, probably of a non-local
nature, to accurately describe such systems. PACS numbers: 31.15.
Density functional theory study of (OCS)2^-
The structural and electronic properties of the carbonyl sulfide dimer anion
are calculated using density functional theory within a pseudopotential method.
Three geometries are optimized and investigated: C2v and C2 symmetric, as well
as one asymmetric structure. A distribution of an excess charge in three
isomers are studied by the Hirshfeld method. In an asymmetric (OCS)2^- isomer
the charge is not equally divided between the two moieties, but it is
distributed as OCS^{-0.6} OCS^{-0.4}. Low-lying excitation levels of three
isomers are compared using the time-dependent density functional theory in the
Casida approach.Comment: pdf (included all figures):
http://www.phy.hr/~goranka/Research/ocs.pd
Supercell technique for total-energy calculations of finite charged and polar systems
We study the behavior of total-energy supercell calculations for dipolar molecules and charged clusters. Using a cutoff Coulomb interaction within the framework of a plane-wave basis set formalism, with all other aspects of the method (pseudopotentials, basis set, exchange-correlation functional) unchanged, we are able to assess directly the interaction effects present in the supercell technique. We find that the supercell method gives structures and energies in almost total agreement with the results of calculations for finite systems, even for molecules with large dipole moments. We also show that the performance of finite-grid calculations can be improved by allowing a degree of aliasing in the Hartree energy, and by using a reciprocal space definition of the cutoff Coulomb interaction
Electronic structure of the (111) and (-1-1-1) surfaces of cubic BN: A local-density-functional ab initio study
We present ab initio local-density-functional electronic structure
calculations for the (111) and (-1-1-1) surfaces of cubic BN. The energetically
stable reconstructions, namely the N adatom, N3 triangle models on the (111),
the (2x1), boron and nitrogen triangle patterns on the (-1-1-1) surface are
investigated. Band structure and properties of the surface states are discussed
in detail.Comment: 8 pages, 12 figure
Is manganese-doped diamond a ferromagnetic semiconductor?
We use density-functional theoretical methods to examine the recent
prediction, based on a mean-field solution of the Zener model, that diamond
doped by Mn (with spin S=5/2) would be a dilute magnetic semiconductor that
remains ferromagnetic well above room temperature. Our findings suggest this to
be unlikely, for four reasons: (1) substitutional Mn in diamond has a low-spin
S=1/2 ground state; (2) the substitutional site is energetically unfavorable
relative to the much larger "divacancy" site; 3) Mn in the divacancy site is an
acceptor, but with only hyperdeep levels, and hence the holes are likely to
remain localized; (4) the calculated Heisenberg couplings between Mn in nearby
divacancy sites are two orders of magnitude smaller than for substitutional Mn
in germanium.Comment: 5 pages, 5 figure
Proof of the thermodynamical stability of the E' center in SiO2
The E' center is a paradigmatic radiation-induced defect in SiO2 whose
peculiar EPR and hyperfine activity has been known since over 40 years. This
center has been traditionally identified with a distorted, positively-charged
oxygen vacancy V_O+. However, no direct proof of the stability of this defect
has ever been provided, so that its identification is still strongly
incomplete. Here we prove directly that distorted V_O+ is metastable and that
it satisfies the key requirements for its identification as E', such as thermal
and optical response, and activation-deactivation mechanisms.Comment: RevTeX 4 pages, 2 figure
Prosocial nudges and visual indicators increase social distancing, but authoritative nudges do not
Social distancing reduces the transmission of COVID-19 and other airborne diseases. To test different ways to increase social distancing, we conducted a field experiment at a major US airport using a system that presented color-coded visual indicators on crowdedness. We complemented those visual indicators with nudges commonly used to increase COVID-19–preventive behaviors. Analyzing data from 57,146 travelers, we find that visual indicators and nudges significantly affected social distancing. Introducing visual indicators increased the share of travelers practicing social distancing, and this positive effect was enhanced by introducing nudges focused on personal benefits (“protect yourself”) and public benefits (“protect others”). Conversely, an authoritative nudge referencing the Centers for Disease Control and Prevention (“don’t break CDC COVID-19 guidelines”) did not change social distancing behavior. Our results demonstrate that visual indicators and informed nudges can boost social distancing and potentially curb the spread of contagious diseases
Ferromagnetism in Mn doped GaAs due to substitutional-interstitial complexes
While most calculations on the properties of the ferromagnetic semiconductor
GaAs:Mn have focussed on isolated Mn substituting the Ga site (Mn), we
investigate here whether alternate lattice sites are favored and what the
magnetic consequences of this might be. Under As-rich (Ga-poor) conditions
prevalent at growth, we find that the formation energies are lower for
Mn over interstitial Mn (Mn).As the Fermi energy is shifted towards
the valence band maximum via external -doping, the formation energy of
Mn is reduced relative to Mn. Furthermore, under epitaxial growth
conditions, the solubility of both substitutional and interstitial Mn are
strongly enhanced over what is possible under bulk growth conditions. The high
concentration of Mn attained under epitaxial growth of p-type material opens
the possibility of Mn atoms forming small clusters. We consider various types
of clusters, including the Coulomb-stabilized clusters involving two Mn
and one Mn. While isolated Mn are hole killers (donors), and therefore
destroy ferromagnetism,complexes such as Mn-Mn-Mn) are found
to be more stable than complexes involving Mn-Mn-Mn. The
former complexes exhibit partial or total quenching of holes, yet Mn in
these complexes provide a channel for a ferromagnetic arrangement of the spins
on the two Mn within the complex. This suggests that ferromagnetism in
Mn doped GaAs arises both from holes due to isolated Mn as well as from
strongly Coulomb stabilized Mn-Mn-Mn clusters.Comment: 7 figure
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