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Distinctive from conventional electronic structure methods, we solve the Schrödinger wave equations of the helium atom and its isoelectronic ions by employing one-dimensional basis functions to separate components. We use full two-electron six-dimensional operators and wavefunctions represented with real-space grids where the refinement of the latter is carried out using a residual minimization method. In contrast to the standard single-electron approach, the current approach results in exact treatment of repulsion energy and, hence, more accurate electron correlation within five centihartrees or better included, with moderate computational cost. A simple numerical convergence between the error to accurate results and the grid-spacing size is found. The obtained two-electron Schrödinger wavefunction that contains vast and elaborating information for the radial correlation function and common one-dimensional functions shows the electron correlation effect on one-electron distributions. [ABSTRACT FROM AUTHOR]

Electronic structures and related properties of a defective endohedral metallofullerene U2@C61-Def[5,6] are studied using density functional theory. It is shown that unlike the U2@C61-Def[6,6] which has a nonet ground state, the U2@C61-Def[5,6] has a quintet ground spin state with a lower total energy than the U2@C61-Def[6,6]. This is due to the antiferromagnetic coupling of the net spin electrons of the U2 unit with the net spin of both the cage and the adatom. Compared with the U2@C60, the [5,6]-type defect demonstrates almost no change in the energy gap, while the [6,6]-type defect does show a reduction. The electronic states and energy gaps of the endohedral metallofullerenes can therefore be engineered in a controllable manner by introducing different adatom-type defects. [ABSTRACT FROM AUTHOR]

First-principlescalculations based on density functional theory have been performedto explore the stable configurations, electronic structures, and vibrationalspectra of neutral and charged silicon monoxide clusters (SiO)n(0,±)(n= 2–7), which could be used as precursors in the synthesisof silicon nanowires. Our theoretical calculations provide new resultson characteristic electron affinity, ionization potential, and vibrationalspectroscopy, guiding future experiments in the synthesis of high-qualitysilicon nanowires. Specifically, as the number of SiO units nincreases, IR spectra of (SiO)n±and Raman spectra of (SiO)n–show an evident blue shift, and Raman spectraof (SiO)ndemonstrate a red shift. Moreover,most of the neutral silicon monoxide clusters have strong IR intensitiesand weak Raman activities, while most of the anionic counterpartshave relatively weak IR intensities and strong Raman activities. Someother energetically competitive isomers of some (SiO)n(0,±)species were also studied forcomparison. [ABSTRACT FROM AUTHOR]

The discovery of the covalent-like character of the hydrogen bonding (H-bonding) system [ Science 342, 611(2013)] has promoted a renewal of our understanding of the electronic and geometric structures of water clusters. In this work, based on density functional theory calculations, we show that the preferential formation of a stable quasiplanar structure of (H2O) n( n = 3-6) is closely related to three kinds of delocalized molecular orbitals (MOs; denoted as MO-I, II, and III) of water rings. These originate from the 2p lone pair electrons of oxygen (O), the 2p bond electrons of O and the 1s electrons of H and the 2s electrons of O and 1s electrons of H, respectively. To maximize the orbital overlaps of the three MOs, geometric planarization is needed. The contribution of the orbital interaction is more than 30% in all the water rings according to our energy decomposition analysis, highlighting the considerable covalent-like characters of H-bonds. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]