Volume 133, Issue 2, 14 July 2010
Index of content:
, , and -phases from density functional theory calculations" title="Electronic and magnetic structure of bulk cobalt: The , , and -phases from density functional theory calculations" />
The geometric, electronic and magnetic properties of the three metallic cobalt phases: , , and have been theoretically studied using periodic density functional calculations with generalized gradient approximation (GGA) and plane wave basis set. These results have been compared with those obtained with approach which have shown a noticeable improvement with regard to experimental data. For instance, the cohesive energy values predicted by GGA are overestimated by , whereas underestimate them by 14%–17%. On the other hand, magnetic moment values are underestimated in GGA while are overestimated for approach by almost the same amount. Besides, the introduction of U parameter gives rise to an electronic redistribution in the d-band structure, which leads to variations in the magnetic properties. Moreover, a higher attention has been paid in the study of the electronic and magnetic properties of the -phase that has not described previously. These studies show that this phase posses special properties that could lead to an unusual behavior in magnetic or catalytic applications.
Communications: On the relation between the scalar and tensor exchange-correlation kernels of the time-dependent density-functional theory133(2010); http://dx.doi.org/10.1063/1.3455711View Description Hide Description
The scalar and tensor exchange-correlation (xc) kernels are key ingredients of the time-dependent density functional theory and the time-dependent current density functionaltheory, respectively. We derive a comparatively simple relation between these two kernels under the assumption that the dynamic xc can be considered “weak.” A calculation of the frequency-dependent dielectric function of silicon using this relation in conjunction with Vignale–Kohn demonstrates a potential of our method to account for the dynamic many-body effects within the rigorous scheme of time-dependent density functional theory. Our formula provides a bridge between the scalar , which directly enters many applications, and the tensor which, due to its locality in space, is much easier to approximate.
Communication: Energetics of reaction pathways for reactions of ethenol with the hydroxyl radical: The importance of internal hydrogen bonding at the transition state133(2010); http://dx.doi.org/10.1063/1.3455996View Description Hide Description
We find high multireference character for abstraction of H from the OH group of ethenol (also called vinyl alcohol); therefore we adopt a multireference approach to calculate barrier heights for the various possible reaction channels of . The relative barrier heights of ten possible saddle points for reaction of OH with ethenol are predicted by multireference Møller–Plesset perturbation theory with active spaces based on correlated participating orbitals (CPOs) and CPO plus a correlated orbital . Six barrier heights for abstracting H from a bond range from 3.1 to 7.7 kcal/mol, two barrier heights for abstracting H from an bond are both 6.0 kcal/mol, and two barrier heights for OH addition to the double bond are −1.8 and −2.8 kcal/mol. Thus we expect abstraction at high-temperature and addition at low temperature. The factor that determines which H is most favorable to abstract is an internal hydrogen bond that constitutes part of a six-membered ring at one of the abstraction saddle points; the hydrogen bond contributes about 3 kcal/mol stabilization.