848 research outputs found
Molecular exchange-correlation Kohn-Sham potential and energy density from ab initio first- and second-order density matrices: examples for XH (X=Li, B,F).
The molecular KohnāSham exchangeācorrelation potential vxc and the energy density Īµxc have been constructed from ab initio firstā and secondāorder density matrices for the series XH (X=Li, B, F). The way various effects of electronic structure and electron correlation manifest themselves in the shape of vxc and Īµxc has been analyzed by their decomposition into various components; the potential of the exchangeācorrelation hole, the kinetic component and (in the case of vxc) the āāresponseāā component. The kinetic energy of noninteracting particles Ts, the kinetic part of the exchangeācorrelation energy Tc, and the energy of the highest occupied molecular orbital ĪµN have been obtained with reasonable accuracy and the effect of bond formation on these functionals has been studied
Improved density functional theory results for frequency-dependent polarizabilities, by the use of an exchange-correlation potential with correct asymptotic behavior.
The exchangeācorrelation potentials vxc which are currently fashionable in density functional theory (DFT), such as those obtained from the local density approximation (LDA) or generalized gradient approximations (GGAs), all suffer from incorrect asymptotic behavior. In atomic calculations, this leads to substantial overestimations of both the static polarizability and the frequency dependence of this property. In the present paper, it is shown that the errors in atomic static dipole and quadrupole polarizabilities are reduced by almost an order of magnitude, if a recently proposed model potential with correct Coulombic longārange behavior is used. The frequency dependence is improved similarly. The model potential also removes the overestimation in molecular polarizabilities, leading to slight improvements for average molecular polarizabilities and their frequency dependence. For the polarizability anisotropy we find that the model potential results do not improve over the LDA and GGA results. Our method for calculating frequencyādependent molecular response properties within timeādependent DFT, which we described in more detail elsewhere, is summarized
Local-density approximation for exchange energy functional in excited-state density functional theory
An exchange energy functional is proposed and tested for obtaining a class of
excited-state energies using density functional formalism. The functional is
the excited-state counterpart of the local-density approximation functional for
the ground state. It takes care of the state dependence of the energy
functional and leads to highly accurate excitation energies
Multiscale Modeling of a Nanoelectromechanical Shuttle
In this article, we report a theoretical analysis of a nanoelectromechanical
shuttle based on a multiscale model that combines microscopic electronic
structure data with macroscopic dynamics. The microscopic part utilizes a
(static) density functional description to obtain the energy levels and
orbitals of the shuttling particle together with the forces acting on the
particle. The macroscopic part combines stochastic charge dynamics that
incorporates the microscopically evaluated tunneling rates with a Newtonian
dynamics.
We have applied the multiscale model to describe the shuttling of a single
copper atom between two gold-like jellium electrodes. We find that energy
spectrum and particle surface interaction greatly influence shuttling dynamics;
in the specific example that we studied the shuttling is found to involve only
charge states Q=0 and Q=+e. The system is found to exhibit two quasi-stable
shuttling modes, a fundamental one and an excited one with a larger amplitude
of mechanical motion, with random transitions between them.Comment: 9 pages, 9 figure
Me against who? Male guppies adjust mating behaviour according to their rivalās presence and attractiveness
This work was supported by Portuguese National Funds through FCT (FundaĆ§Ć£o para a CiĆŖncia e a Tecnologia), within the cE3c Unit FCT funding (grant number UID/BIA/00329/2013), IO PhD grant (SFRH/BD/90686/2012) and SAMV (SFRH/BPD/66042/2009 and PTDC/BIAāANM/0810/14) and MB (SFRH/BPD/82259/2011) PostāDoctoral research grants. This work was also supported by the ERC (European Research Council) AdG BioTIME (250189) to AEM.Sexual selection theory suggests that males need to constantly reappraise their mating decisions to take account of the presence and the phenotypes of their rivals. Here we examine this expectation by asking: (i) If the presence of a rival influences male mating behaviour; (ii) How important is the attractiveness of the rival (absolute attractiveness) in shaping male behaviour; and (iii) How does a male's attractiveness in comparison to his rival (relative attractiveness) influence a male's mating decisions. Using the Trinidadian guppy, a species in which female mate choice (based on malesā attractive traits) plays an important role in male mating outcomes, we recorded the frequency of courtship displays and unsolicited attempts by focal males. First, we quantified focal male mating behaviour with and without a rival. Since the probability of a successful mating is, on average, halved by the presence of a rival, we predicted that under competition the focal male would invest more in less costly mating tacticāunsolicited attempts. Second, we examined how the rival's standard length and area of orange coloration mediated focal male mating behaviour. We found that rival presence influenced how focal males responded to females in terms of both mating tactics. However, the rival attractiveness elicited changes only in male courtship display. Focal males increased courtship display rate if his rival was small or if possessed large amounts of orange, regardless of considering rival absolute or relative attractiveness. Our results show that males invest in the costlier mating tactic when there is no rival or in the presence of a smaller rival. Interestingly, they make a similar investment in the presence of an attractive orange rival. Overall, this study highlights the importance of fineāgrained male decisions in mating encounters and shows that mating tactics are differentially shaped by multiple competition risk cues.PostprintPeer reviewe
Homogeneous Gold Catalysis through Relativistic Effects: Addition of Water to Propyne
In the catalytic addition of water to propyne the Au(III) catalyst is not
stable under non-relativistic conditions and dissociates into a Au(I) compound
and Cl2. This implies that one link in the chain of events in the catalytic
cycle is broken and relativity may well be seen as the reason why Au(III)
compounds are effective catalysts.Comment: 12 pages, 3 figures, 1 tabl
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