A function for testing the reliability of long-range electron density in atoms

1979 ◽  
Vol 70 (1) ◽  
pp. 584 ◽  
Author(s):  
Terry S. Carlton
Keyword(s):  
Electron Density ◽  
Long Range

scholarly journals Representation of the QM Subsystem for Long-Range Electrostatic Interaction in Non-Periodic Ab Initio QM/MM Calculations

Molecules ◽  
2018 ◽  
Vol 23 (10) ◽  
pp. 2500 ◽  
Author(s):  
Xiaoliang Pan ◽  
Edina Rosta ◽  
Yihan Shao
Keyword(s):  
Electron Density ◽  
Long Range ◽  
Electrostatic Interactions ◽  
Density Functional ◽  
Switching Function ◽  
Excitation Energies ◽  
Functional Theory ◽  
Vertical Excitation ◽  
Distance Cutoff ◽  
Switching Functions

In QM/MM calculations, it is essential to handle electrostatic interactions between the QM and MM subsystems accurately and efficiently. To achieve maximal efficiency, it is convenient to adopt a hybrid scheme, where the QM electron density is used explicitly in the evaluation of short-range QM/MM electrostatic interactions, while a multipolar representation for the QM electron density is employed to account for the long-range QM/MM electrostatic interactions. In order to avoid energy discontinuity at the cutoffs, which separate the short- and long-range QM/MM electrostatic interactions, a switching function should be utilized to ensure a smooth potential energy surface. In this study, we benchmarked the accuracy of such hybrid embedding schemes for QM/MM electrostatic interactions using different multipolar representations, switching functions and cutoff distances. For test systems (neutral and anionic oxyluciferin in MM (aqueous and enzyme) environments), the best accuracy was acquired with a combination of QM electrostatic potential (ESP) charges and dipoles and two switching functions (long-range electrostatic corrections (LREC) and Switch) in the treatment of long-range QM/MM electrostatics. It allowed us to apply a 10Å distance cutoff and still obtain QM/MM electrostatics/polarization energies within 0.1 kcal/mol and time-dependent density functional theory (TDDFT)/MM vertical excitation energies within 10−3 eV from theoretical reference values.

Tungsten carbonyl complexes of Main Group IV organometallic sulfides

1983 ◽  
Vol 61 (6) ◽  
pp. 1096-1099 ◽  
Author(s):  
C. Robert Lucas
Keyword(s):  
Electron Density ◽  
Long Range ◽  
Spectroscopic Data ◽  
Spectroscopic Properties ◽  
Group Iv ◽  
Carbonyl Complexes ◽  
Multiple Bonds ◽  
Organic Systems ◽  
Tungsten Carbonyl ◽  
New Compounds

Vibrational spectroscopic data from the literature and from seven new compounds is treated by the methods of Cotton and Kraihanzel and of Graham. The results are interpreted as evidence that in (R3MSPh)W(CO)5 (R = Me, Ph: M = Si, Ge, Sn) there are W → S dπ–dπ and S → M pπ → dπ components to the bonding, the extent of the latter varying in the order Si > Ge > Sn. It is concluded that changes in the carbonyl stretching spectra reflect changes in electron density on sulfur. Thus, the carbonyl spectra are affected both by the electronegativity of groups bound to sulfur and by the extent of S → M π-bonding. The fact that changing M affects spectroscopic properties of a bond three atoms away represents long range transmission of effects via multiple bonds but in a manner quite unlike that in conjugated organic systems.

White-Light Coronal Structures: Streamers and CMEs

1994 ◽  
Vol 144 ◽  
pp. 82
Author(s):  
E. Hildner
Keyword(s):  
Emission Line ◽  
Electron Density ◽  
White Light ◽  
Coronal Mass Ejections ◽  
X Rays ◽  
Solar Cycles ◽  
Temperature Function ◽  
X Ray ◽  
Eclipse Observations ◽  
Coronal Structures

AbstractOver the last twenty years, orbiting coronagraphs have vastly increased the amount of observational material for the whitelight corona. Spanning almost two solar cycles, and augmented by ground-based K-coronameter, emission-line, and eclipse observations, these data allow us to assess,inter alia: the typical and atypical behavior of the corona; how the corona evolves on time scales from minutes to a decade; and (in some respects) the relation between photospheric, coronal, and interplanetary features. This talk will review recent results on these three topics. A remark or two will attempt to relate the whitelight corona between 1.5 and 6 R⊙to the corona seen at lower altitudes in soft X-rays (e.g., with Yohkoh). The whitelight emission depends only on integrated electron density independent of temperature, whereas the soft X-ray emission depends upon the integral of electron density squared times a temperature function. The properties of coronal mass ejections (CMEs) will be reviewed briefly and their relationships to other solar and interplanetary phenomena will be noted.

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