scholarly journals Application of new method in quantum-mechanical calculations of the structural properties and the formation energy of the ordered Mu - phase in the Fe - Mo system

2021 ◽  
Vol 2052 (1) ◽  
pp. 012048
Author(s):  
A L Udovsky ◽  
D A Vasilyev
Keyword(s):  
Total Energy ◽  
Formation Energy ◽  
Plane Waves ◽  
Quantum Mechanical ◽  
Quantum Mechanical Calculations ◽  
Minimum Total Energy ◽  
A New Technique ◽  
Formation Energies ◽  
Crystal Lattice Parameters ◽  
Account Relaxation

Abstract A new technique of finding the minimum total energy, calculated by quantum mechanical calculations, for hexagonal Mu- (μ-) phases of stoichiometric compositions taking into account relaxation, as well as optimized crystal lattice parameters for different compositions in the Fe-Mo system, has been applied. The convergence of the total energy is investigated as a function of the number of plane waves (k) in the range 2000 ÷ 105. Differences in the structural energies between bcc, C14 Laves and μ- phases of pure components, as well as the formation energies of μ- phases of stoichiometric compositions Fe9Mo4, Fe7Mo6 and Fe6Mo7 are calculated.

scholarly journals Application of super cells for quantum-mechanical calculations of the mixing enthalpy of the BCC-phase of the Fe-V system for the basic state

2021 ◽  
Vol 2052 (1) ◽  
pp. 012049
Author(s):  
A L Udovsky ◽  
M V Kupavtsev
Keyword(s):  
Total Energy ◽  
Ground State ◽  
Ferromagnetic State ◽  
Mixing Enthalpy ◽  
Quantum Mechanical ◽  
Quantum Mechanical Calculations ◽  
Bcc Phase

Abstract In this work, the super-cells were used for quantum mechanical calculations of the mixing enthalpia of the BCC phase of the Fe-V system for the ground state. The values of total energy were calculated using 16 -th and 54- atomic super-cells for both clean components and alloys. The mixing enthalpy (ΔH) for the BCC phase was calculated on four 16- and 54- atomic super-cells in the vicinity of pure components, on the basis of which the dependence of the concentration ΔH for BCC alloys in the ferromagnetic state of the Fe-V system of the ground state was built.

Structural Study of Dopamine Agonist Lisuride

2003 ◽  
Vol 68 (11) ◽  
pp. 2150-2158
Author(s):  
Jan Čejka ◽  
Bohumil Kratochvíl ◽  
Stanislav Böhm ◽  
Ivana Císařová ◽  
Ladislav Cvak ◽  
...  
Keyword(s):  
Total Energy ◽  
Dopamine Agonist ◽  
Ergot Alkaloid ◽  
Simplified Model ◽  
Side Chain ◽  
Quantum Mechanical ◽  
Quantum Mechanical Calculations ◽  
Conformation Analysis ◽  
X Ray Diffraction ◽  
X Ray

One monoclinic and three orthorhombic structures of natural ergot alkaloid lisuride were solved by X-ray diffraction techniques. The conformation analysis has revealed that side chain orientations of lisuride differ significantly from those observed in related terguride (trans-dihydrolisuride). The conformation found in individual lisuride molecules corresponds to another minimum of total energy calculated by ab initio quantum-mechanical calculations for a simplified model of 3-(cyclohex-2-en-1-yl)-1,1-diethylurea.

Crystal Forms of Semisynthetic Ergot Alkaloid Terguride

2002 ◽  
Vol 67 (4) ◽  
pp. 479-489 ◽  
Author(s):  
Michal Hušák ◽  
Bohumil Kratochvíl ◽  
Ivana Císařová ◽  
Ladislav Cvak ◽  
Alexandr Jegorov ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Ergot Alkaloid ◽  
Simplified Model ◽  
Quantum Mechanical ◽  
Quantum Mechanical Calculations ◽  
X Ray Diffraction ◽  
Torsion Angles ◽  
Crystal Forms ◽  
X Ray ◽  
Independent Molecules

Two new structures of semisynthetic ergot alkaloid terguride created by unusual number of symmetry-independent molecules were determined by X-ray diffraction methods at 150 K. Form A (monoclinic, P212121, Z = 12) contains three symmetry-independent terguride molecules and two molecules of water in the asymmetric part of the unit cell. The form CA (monoclinic, P21, Z = 8) is an anhydrate remarkable by the presence of four symmetry-independent molecules in the crystal structure. Conformations of twelve symmetry-independent molecules that were found in four already described terguride structures are compared with torsion angles obtained by ab initio quantum-mechanical calculations for the simplified model of N-cyclohexyl-N'-diethylurea.

Chemical accuracy from ‘Coulomb hole’ extrapolated molecular quantum-mechanical calculations

2001 ◽  
Vol 567-568 ◽  
pp. 375-384 ◽  
Author(s):  
K.L Bak ◽  
A Halkier ◽  
P Jørgensen ◽  
J Olsen ◽  
T Helgaker ◽  
...  
Keyword(s):  
Quantum Mechanical ◽  
Quantum Mechanical Calculations ◽  
Coulomb Hole
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