Nonlocal density functional theory [DFT] has been used to compute vibrational frequencies and intensities of nickel porphine and of several isotopomers via a scaled quantum mechanical [SQM] force field [FF]. The results support and extend those obtained from a revised empirical FF. The force constants are similar for the two FF's, although the SQM FF has a complete set of off-diagonal elements. The SQM FF produces somewhat more accurate frequencies and isotope shifts than the empirical FF for the in-plane NiP modes. In addition, the SQM FF calculates out-of-plane modes that are in good agreement with available infrared [IR] data. Also, the SQM FF satisfactorily reproduces the relative intensities of both IR and [off-resonance] Raman bands. A striking result is the calculation of large Raman intensities for nontotally symmetric B1g modes, in conformity with experimental FT-Raman spectra. This effect is attributed to the phasing of local polarizability components of the pyrrole rings and methine bonds. The DFT-computed bond distances and angles are in good agreement with crystallographically determined values. The lowest energy structure is a true minimum with D2d symmetry. It is slightly distorted from the planar geometry along the ruffling coordinate. Constraining it to be planar [D4h] raises the energy slightly [∼0.1 kcal/mol] and leads to an imaginary frequency for the ruffling mode. This finding provides theoretical confirmation of Hoard's empirical observation that metal ions with M−N[pyrrole] bonds significantly shorter than 2.00 Å produce an out-of-plane distortion of the macrocycle. The computed degree of ruffling is small, as are the calculated shifts in vibrational frequencies [<6 cm-1]. Although the symmetry lowering relaxes selection rules, the induced intensity in IR- or Raman-forbidden modes is calculated to be negligible, except for a single IR band associated with an out-of-plane mode [Eg, 420 cm-1], which is indeed observed experimentally. The agreement of both frequencies and intensities with experiment provides further validation of the accuracy of the DFT, even for molecules as complex as metalloporphyrins.
Abstract Evapotranspiration (ET), a key component of the hydrological cycle, affects the transport of water and energy in the soil–vegetation–atmosphere system. Thus, quantifying the driving forces of ET dynamics is important to ensure rational water resource utilization. Based on meteorological and satellite data, spatiotemporal dynamics of ET were detected using the Surface Energy Balance System (SEBS) model, and effects of climate variability and landscape pattern change on ET dynamics in an arid to semiarid landscape mosaic during the growing season (April‐October) from 2001 to 2015 in Xilingol League, China were evaluated. The results indicated that (a) a significant increase (P < .05) in ET was found in the north‐eastern Xilingol League, and a significant decrease (P < .05) in ET was confined to the southwest and (b) climate variability had significant effects on ET dynamics. All climatic factors showed a positive correlation relationship with ET dynamics, and mean temperature (Ta) was the most influential climatic factor on ET dynamics followed by relative humidity (Rh), wind speed (Ws), and precipitation (Pr), respectively. The influence of landscape pattern change on ET dynamics was mainly reflected in the increase of the normalized difference vegetation index (NDVI) promoting ET dynamics. Several other landscape pattern metrics also had important impacts on ET dynamics, which were mainly reflected in the positive effect of the aggregation index (AI) on ET dynamics and the negative effects of the largest patch index (LPI), edge density (ED), and percentage of landscape (PLAND) on ET dynamics. To promote effective water resource utilization, landscape managers should continue to moderately implement vegetation restoration projects such as the Grain for Green Project, orient with conversion of low‐quality cropland into grassland, and conserve large areas of grassland. Appropriate management measures for forests and cropland scattered in the landscape mosaic, based on local climate and soil properties, as well as socioeconomic goals, are also required.
The electrical resistivity of TiB2 has been measured using a DIA-6 cubic anvil apparatus at pressures up to 8 GPa and temperatures up to 800 K. The ambient-condition resistivity is determined to be 13.3 (±0.9) μΩ cm. The resistivity decreases with increasing pressure. At pressures above 2 GPa, the pressure dependence of the resistivity is about −0.36 μΩ cm/GPa. On heating, the resistivity increases linearly with temperature. The measurements at simultaneously high pressure (3.2 GPa) and high temperatures yield a temperature dependence of 46 (±5) nΩ cm/K for the resistivity.
Abstract. As the theoretical upper bound of evapotranspiration (ET) or water use by ecosystems, potential ET (PET) has always been widely used as a variable linking a variety of disciplines, such as climatology, ecology, hydrology, and agronomy. However, substantial uncertainties exist in the current PET methods (e.g., empiric models and single-layer models) and datasets, because of unrealistic configurations of land surface and unreasonable parameterizations. Therefore, this study comprehensively considered interspecific differences in various vegetation-related parameters (e.g., plant stomatal resistance and CO2 effects on stomatal resistance) to calibrate and parametrize the Shuttleworth-Wallace (SW) model for forests, shrubland, grassland and cropland. We derived the parameters using identified daily ET observations with no water stress (i.e., PET) at 96 eddy covariance (EC) sites across the globe. Model validations suggest that the calibrated model could be transferable from known observations to any location. Based on four popular meteorological datasets, relatively realistic canopy height and time-varying land use/land cover and Leaf Area Index, we generated a global 5 km ensemble mean monthly PET dataset that includes two components of potential transpiration (PT) and soil evaporation (PE) for the 1982–2015 time period. Using this new dataset, the climatological characteristics of PET partitioning and the spatio-temporal changes in PET, PE and PT were investigated. The global mean annual PET was 1200 mm with PT/PET of 40 % and PE/PET of 60 %, and moreover controlled by PT and PE over 43 % and 57 % of the globe, respectively. Globally, the annual PET and PT significantly (p<0.05) increases by 1.25 mm/yr and 1.22 mm/yr over the last 34 years, followed by a slight increase in the annual PE. Overall, the annual PET changes over 53 % of the globe could be attributed to PT, and the rest to PE. The new PET dataset may be used by academic communities and various agencies to conduct climatological analyses, hydrological modelling, drought studies, agricultural water management, and biodiversity conservation. The dataset is available at https://doi.org/10.11888/Terre.tpdc.300193 (Sun et al., 2023).
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