Magnetic ordering, electronic structure and magnetic anisotropy energy in the high-spin Mn10_{10} single molecule magnet

We report the electronic structure and magnetic ordering of the single molecule magnet [Mn$_{10}$O$_{4}$(2,2'-biphenoxide)$_{4}$Br$_{12}$]$^{4-}$ based on first-principles all-electron density-functional calculations. We find that two of the ten core Mn atoms are coupled antiferromagnetically to the remaining eight, resulting in a ferrimagnetic ground state with total spin S=13. The calculated magnetic anisotropy barrier is found to be 9 K in good agreement with experiment. The presence of the Br anions impact the electronic structure and therefore the magnetic properties of the 10 Mn atoms. However, the electric field due to the negative charges has no significant effect on the magnetic anisotropy.Comment: 4 pages, submitted to PR

The Financial Status of North Dakota Farmers and Ranchers: January 1, 1985, Survey Results

Agricultural Finance,

The Hamiltonian of the V15_{15} Spin System from first-principles Density-Functional Calculations

We report first-principles all-electron density-functional based studies of the electronic structure, magnetic ordering and anisotropy for the V$_{15}$ molecular magnet. From these calculations, we determine a Heisenberg Hamiltonian with four antiferromagnetic and one {\em ferromagnetic} coupling. We perform direct diagonalization to determine the temperature dependence of the susceptibility. This Hamiltonian reproduces the experimentally observed spin $S$=1/2 ground state and low-lying $S$=3/2 excited state. A small anisotropy term is necessary to account for the temperature independent part of the magnetization curve.Comment: 4 pages in RevTeX format + 2 ps-figures, accepted by PRL Feb. 2001 (previous version was an older version of the paper

DFT calculation of the intermolecular exchange interaction in the magnetic Mn4_4 dimer

The dimeric form of the single-molecule magnet [Mn$_4$O$_3$Cl$_4$(O$_2$CEt)$_3$(py)$_3$]$_2$ recently revealed interesting phenomena: no quantum tunneling at zero field and tunneling before magnetic field reversal. This is attributed to substantial antiferromagnetic exchange interaction between different monomers. The intermolecular exchange interaction, electronic structure and magnetic properties of this molecular magnet are calculated using density-functional theory within generalized-gradient approximation. Calculations are in good agreement with experiment.Comment: 4 page

Muscle Activation in Individuals Who are Status-Post a Stroke during Over Ground, Treadmill, and Body Weight Supported Gait: A Comparative Study

Purpose: The purpose of this study was to evaluate individuals who are status post stroke during ambulation over ground, on a treadmill without support, and on a treadmill with partial body weight support (PBWS) to determine if there are any differences in muscle activation of major muscle groups in the lower extremity. Subjects: Two subjects were recruited for this study. Subjects were included if they were over the age of 50 years, could fulfill a two-hour time commitment, and walk independently with or without the use of an assistive device. Subjects were excluded if they have had surgery or an existing orthopedic involvement of the lower extremities. Instrumentation: Sensor surface electrodes were used to pick up electromyography (EMG) activity. EMG activity was collected and final data is presented as percent of normalized EMG activity as an average of four to five gait cycles for each of the support trials. Procedure: Consent forms were reviewed and signed by each participant. Electrodes and a heel switch were placed on the involved lower extremity. Subjects performed two trial walks over level ground. Subjects also performed three treadmill ambulation conditions in random order: ambulation on the treadmill without a harness (trm), ambulation on the treadmill with a harness and no body weight support (trmh), and ambulation on the treadmill with a harness and PBWS of 15% (trms). Subjects ambulated for two minutes and EMG activity was recorded for 30 seconds at the end of each minute during each trial condition. Data Analysis: The mean EMG activity of the second trial for all ambulation conditions was calculated for both stance and swing phases of each subject. Descriptive statistics were then used to compare muscle activation across conditions, as well as rank EMG mean muscle activity for each trial condition from highest to lowest. Results: EMG rankings were inconsistent across conditions, but both subjects had the least gastrocnemius activity during the trms condition. Conclusion and Clinical Implication: There were no major findings or trends to suggest differences or similarities in muscle activation between any of the conditions for either subject. Therefore, further research is needed

Coulomb parameters and photoemission for the molecular metal TTF-TCNQ

We employ density-functional theory to calculate realistic parameters for an extended Hubbard model of the molecular metal TTF-TCNQ. Considering both intra- and intermolecular screening in the crystal, we find significant longer-range Coulomb interactions along the molecular stacks, as well as inter-stack coupling. We show that the long-range Coulomb term of the extended Hubbard model leads to a broadening of the spectral density, likely resolving the problems with the interpretation of photoemission experiments using a simple Hubbard model only.Comment: 4 pages, 2 figure

Crop Rotation Effects on N03-N Leaching and Corn Yields Under Manure Management Practices

Nonpoint source nutrient pollution is recognized as an important environmental and social issue for several reasons. First, manure from swine production facilities can have serious impacts on the quality of surface and ground water resources. Second, several states are in the process of creating laws to reduce nitrogen and phosphorus loadings from manure to soil and water resources. Third, pollution of water resources from nutrients supplied by manure to croplands will set parameters for developing public policies on the management of manure

Predicted Infrared and Raman Spectra for Neutral Ti_8C_12 Isomers

Using a density-functional based algorithm, the full IR and Raman spectra are calculated for the neutral Ti_8C_12 cluster assuming geometries of Th, Td, D2d and C3v symmetry. The Th pentagonal dodecahedron is found to be dynamically unstable. The calculated properties of the relaxed structure having C3v symmetry are found to be in excellent agreement with experimental gas phase infrared results, ionization potential and electron affinity measurements. Consequently, the results presented may be used as a reference for further experimental characterization using vibrational spectroscopy.Comment: 6 pages, 5 figures. Physical Review A, 2002 (in press

Negative differential resistance in molecular junctions: The effect of the electrodes electronic structure

We have carried out calculations of electron transport through a metal-molecule-metal junction with metal nanoclusters taking the part of electrodes. We show that negative differential resistance peaks could appear in the current-voltage curves. The peaks arise due to narrow features in the electron density of states of the metal clusters. The proposed analysis is based on the ab initio computations of the relevant wave functions and energies within the framework of the density functional theory using NRLMOL software package.Comment: 4 pages, 2 figures, added text