Nonlocal-density-functional bond-energy calculations of cage-shaped carbon fullerenes:C32andC60

1992 ◽  
Vol 45 (23) ◽  
pp. 13690-13693 ◽  
Author(s):  
Kinya Kobayashi ◽  
Noriyuki Kurita ◽  
Hiroki Kumahora ◽  
Kazutami Tago ◽  
Kunio Ozawa
Keyword(s):  
Bond Energy ◽  
Density Functional ◽  
Energy Calculations

scholarly journals Density-functional Based Tight-binding Calculations on Thiophene Polymorphism

VLSI Design ◽  
2001 ◽  
Vol 13 (1-4) ◽  
pp. 393-397
Author(s):  
J. Widany ◽  
G. Daminelli ◽  
A. Di Carlo ◽  
P. Lugli
Keyword(s):  
Total Energy ◽  
Intermolecular Interaction ◽  
Density Functional ◽  
Tight Binding ◽  
Methyl Groups ◽  
Direct Function ◽  
Energy Calculations ◽  
Polymorphic Modifications

Total energy calculations based on a density-functional tight-binding scheme have been performed on polymorphic modifications of various thiophene crystals. The investigated structures include sulphanyl-substituted quater-thiophene and methyl-substituted sexithiophene, in the monoclinic and triclinic modifications. Attention has been focused on the intermolecular interaction between the molecular units. Despite the similarities in the backbone geometries, the strength and nature of intermolecular interaction differs largely in the various polymorphs. Sulphur atoms belonging to the thiophene rings are strongly involved in the interaction. Sulphanyl substituents play an important role, while methyl groups do not contribute. The strength of intermolecular interaction is not a direct function of atom distance.

scholarly journals Ab Initio High-Pressure Study of Semiconductor-Metal Phase Transition of the Chalcogenide Compound KPSe6

2020 ◽  
Vol 2020 ◽  
pp. 1-9 ◽  
Author(s):  
P. O. Jomo ◽  
C. O. Otieno ◽  
P. W. O. Nyawere
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Ab Initio ◽  
Density Functional ◽  
Basis Sets ◽  
Metal Phase ◽  
Generalized Gradient ◽  
Energy Calculations ◽  
Metal Phase Transition ◽  
Chalcogenide Compound

We report the results of pressure-induced semiconductor-metal phase transition of the semiconducting chalcogenide compound KPSe6 under high pressure using the ab initio methods. The ground-state energy calculations were performed within density functional theory and the generalized gradient approximation using the pseudopotential method with plane-wave basis sets. The projector augmented-wave (PAW) pseudopotentials were used in our calculation. The optimized lattice parameters were found from total energy calculations as 13 Bohr, 1.6 Bohr, and 1.8 Bohr for cell dimensions one, two, and three, respectively, which are in good agreement with experimental calculations. At zero pressure, the material portrayed a semiconducting property with a direct bandgap of ≈1.7 eV. As we subjected the material to pressure, the band gap was observed to reduce until it disappeared. The phase transition from the semiconductor to metal was found to occur at ∼45 GPa, implying that the material underwent metallization as pressure was increased further.

Polymorphism in two biologically active dihydropyrimidinium hydrochloride derivatives: quantitative inputs towards the energetics associated with crystal packing

2014 ◽  
Vol 70 (4) ◽  
pp. 681-696 ◽  
Author(s):  
Piyush Panini ◽  
K. N. Venugopala ◽  
Bharti Odhav ◽  
Deepak Chopra
Keyword(s):  
Hydrogen Bonds ◽  
Intermolecular Interactions ◽  
Density Functional ◽  
Crystal Packing ◽  
Lattice Energy ◽  
Biologically Active ◽  
Two Dimensional ◽  
Energy Calculations ◽  
X Ray ◽  
Fingerprint Plots

A new polymorph belonging to the tetrahydropyrimidinium class of compounds, namely 6-(4-chlorophenyl)-5-(methoxycarbonyl)-4-methyl-2-(3-(trifluoromethylthio)phenylamino)-3,6-dihydropyrimidin-1-ium chloride, and a hydrate of 2-(3-bromophenylamino)-6-(4-chlorophenyl)-5-(methoxycarbonyl)-4-methyl-3,6-dihydropyrimidin-1-ium chloride, have been isolated and characterized using single-crystal X-ray diffraction (XRD). A detailed comprehensive analysis of the crystal packing in terms of the associated intermolecular interactions and a quantification of their interaction energies have been performed for both forms of the two different organic salts (AandB) using X-ray crystallography and computational methods such as density functional theory (DFT) quantum mechanical calculations, PIXEL lattice-energy calculations (with decomposition of total lattice energy into the Coulombic, polarization, dispersion and repulsion contribution), the calculation of the Madelung constant (the EUGEN method), Hirshfeld and two-dimensional fingerprint plots. The presence of ionic [N—H]+...Cl−and [C—H]+...Cl−hydrogen bonds mainly stabilizes the crystal packing in both formsAandB, while in the case ofB·H2O [N—H]+...Owaterand Owater—H...Cl−hydrogen bonds along with [N—H]+...Cl−and [C—H]+...Cl−provide stability to the crystal packing. The lattice-energy calculations from both PIXEL and EUGEN methods revealed that in the case ofA, form (I) (monoclinic) is more stable whereas forBit is the anhydrous form that is more stable. The analysis of the `Madelung mode' of crystal packing of two forms ofAandBand its hydrates suggest that differences exist in the position of the charged ions/atoms in the organic solid state. TheR/E(distance–energy) plots for all the crystal structures show that the molecular pairs in their crystal packing are connected with either highly stabilizing (due to the presence of organicR+and Cl−) or highly destabilizing Coulombic contacts. The difference in crystal packing and associated intermolecular interactions between polymorphs (in the case ofA) or the hydrates (in the case ofB) have been clearly elucidated by the analysis of Hirshfeld surfaces and two-dimensional fingerprint plots. The relative contributions of the various interactions to the Hirshfeld surface for the cationic (dihydropyrimidinium) part and anionic (chloride ion) part for the two forms ofAandBand its hydrate were observed to be different.

A Comparison of the Lewis Basicity of Diamidocarbenes and Diaminocarbenes

2015 ◽  
Vol 68 (7) ◽  
pp. 1084 ◽  
Author(s):  
Chin-Hung Lai
Keyword(s):  
Density Functional Theory ◽  
Lewis Acid ◽  
Base Pair ◽  
Bond Energy ◽  
Density Functional ◽  
Hydrogen Abstraction ◽  
Density Functional Theory Calculations ◽  
Acid Base ◽  
Functional Theory ◽  
The Density Functional Theory

In this study, density functional theory calculations, using the M06-2X functional, were performed to investigate the efficiencies of various carbenes in inducing hydrogen abstraction in BH3 through the formation of a Lewis acid–base pair with BH3. The density functional theory results indicate that diamidocarbenes are more efficient in reducing the B–H bond energy of BH3 than diaminocarbenes. Natural bond orbital and combined charge and bond energy analyses were performed to investigate the Lewis acid–base pair formed by BH3 and the title carbenes.

Bond-Energy and Surface-Energy Calculations in Metals

2010 ◽  
Vol 87 (6) ◽  
pp. 608-612 ◽  
Author(s):  
James G. Eberhart ◽  
Steve Horner
Keyword(s):  
Surface Energy ◽  
Bond Energy ◽  
Energy Calculations
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