scholarly journals Use of bond-valence sums in modelling the diffuse scattering from PZN (PbZn1/3Nb2/3O3)

2014 ◽  
Vol 70 (6) ◽  
pp. 626-635 ◽  
Author(s):  
R. E. Whitfield ◽  
T. R. Welberry ◽  
M. Paściak ◽  
D. J. Goossens
Keyword(s):  
Diffuse Scattering ◽  
Density Functional ◽  
Minimum Energy ◽  
Bond Valence ◽  
Instability Index ◽  
Global Instability ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Bond Valence Sum ◽  
Order Structures

This work extends previous efforts to model diffuse scattering from PZN (PbZn1/3Nb2/3O3). Earlier work [Welberryet al.(2005).J. Appl. Cryst.38, 639–647; Welberryet al.(2006).Phys. Rev. B,74, 224108] is highly prescriptive, using Monte Carlo simulation with very artificial potentials to induce short-range-order structures which were deduced as necessary from inspection of the data. While this gives valid results for the nature of the local structure, it does not strongly relate these structures to underlying crystal chemistry. In that work, the idea of the bond-valence sum was used as a guide to the expected behaviour of the atoms. This paper extends the use of the bond-valence sum from a qualitative guide to becoming a key aspect of the potential experienced by the atoms, through the idea of the global instability index, whose square has been shown to be proportional to the density functional theory energy of some systems when close to the minimum energy configuration.

scholarly journals A NOVEL FRACTAL GEOMETRY DOPING FOR GRAPHENE NANORIBBON AND THE OPTIMIZATION OF CRYSTAL: A DENSITY FUNCTIONAL THEORY (DFT) STUDY

2020 ◽  
Vol 17 (35) ◽  
pp. 1148-1158
Author(s):  
Mohammed L. JABBAR ◽  
Kadhum J. AL-SHEJAIRY
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Energy Gap ◽  
Minimum Energy ◽  
Graphene Nanoribbon ◽  
Chemical Doping ◽  
Functional Theory ◽  
Lower Reactivity ◽  
The Density Functional Theory ◽  
Semiconductor Behavior

Chemical doping is a promising route to engineering and controlling the electronic properties of the zigzag graphene nanoribbon (ZGNR). By using the first-principles of the density functional theory (DFT) calculations at the B3LYP/ 6-31G, which implemented in the Gaussian 09 software, various properties, such as the geometrical structure, DOS, HOMO, LUMO infrared spectra, and energy gap of the ZGNR, were investigated with various sites and concentrations of the phosphorus (P). It was observed that the ZGNR could be converted from linear to fractal dimension by using phosphorus (P) impurities. Also, the fractal binary tree of the ZGNR and P-ZGNR structures is a highlight. The results demonstrated that the energy gap has different values, which located at this range from 0.51eV to 1.158 eV for pristine ZGNR and P-ZGNR structures. This range of energy gap is variable according to the use of GNRs in any apparatus. Then, the P-ZGNR has semiconductor behavior. Moreover, there are no imaginary wavenumbers on the evaluated vibrational spectrum confirms that the model corresponds to minimum energy. Then, these results make P-ZGNR can be utilized in various applications due to this structure became more stable and lower reactivity.

Conformation and electronic structure of Carbidopa. A QM/MD study

2016 ◽  
Vol 15 (01) ◽  
pp. 1650002
Author(s):  
Ghader M. Sukker ◽  
Nuha Wazzan ◽  
Ashour Ahmed ◽  
Rifaat Hilal
Keyword(s):  
Density Functional ◽  
Minimum Energy ◽  
Geometry Optimization ◽  
Md Simulations ◽  
Energy Structure ◽  
Functional Theory ◽  
Conformational Preferences ◽  
The Density Functional Theory ◽  
Quantum Chemical Topology ◽  
Bonding Characteristics

Carbidopa (CD) is a drug used in combination with L-dopa (LD) in treatment of Parkinson’s disease (PD). CD is an inhibitor for enzyme decarboxylase, yet its mode of action is not entirely known although it is believed to involve enzyme shape recognition. The present work attempts to investigate the conformational preferences of CD. Tight geometry optimization at the density functional theory (DFT)/B3LYP/6-311[Formula: see text]G** level of theory has been carried out. The shallow nature of the potential energy surface (PES) and the presence of several local minima within a small energy range necessitate the launching of DFT-based molecular dynamics (MD) simulations. Two MD experiments were submitted for 35,000 points each. The complete trajectory in time domain of 10.5 ps is analyzed and discussed. The global minimum energy structure of CD is localized and identified by subsequent frequency calculations. The quantum theory of atom in molecules (QTAIMs) is used to extract and compare the quantum chemical topology features of the electron density distribution in CD and LD. Bonding characteristics are analyzed and discussed within the natural bond orbital (NBO) framework.

scholarly journals Investigation of the absorption of CO2 in ionic liquid

2016 ◽  
Vol 29 (1) ◽  
pp. 41-46
Author(s):  
Kalyan Dhar ◽  
Syed Fahim
Keyword(s):  
Ionic Liquid ◽  
Binding Sites ◽  
Density Functional ◽  
Room Temperature ◽  
Minimum Energy ◽  
Environmental Concerns ◽  
Co2 Absorption ◽  
Solvation Model ◽  
Functional Theory ◽  
The Density Functional Theory

Due to environmental concerns, current interest is the development of technologies that may be able to remove CO2 efficiently from exhaust gases and thus avoid its dispersion in the atmosphere. The density functional theory (DFT) calculations with the modern continuum solvation model (IEFPCM-SMD) was used to study the mechanism of CO2 absorption in room temperature ionic liquid such as, [EMIM][BF4] (1-ethyl-3- methylimidazolium tetrafluoroborate). We determine the minimum energy structures and to determine the possible binding sites for CO2 absorption process in [EMIM][BF4]; by comparing the relative minimum energy of [EMIM][BF4] in the presence and absence of CO2.Bangladesh J. Sci. Res. 29(1): 41-46, June-2016

Study of Elastic Properies of Ti3Al Intermetallic Compound Using the Ab Initio Calculation

2014 ◽  
Vol 805 ◽  
pp. 690-693
Author(s):  
Carlos Alberto Soufen ◽  
Marcelo Capella de Campos ◽  
Carlos Alberto Fonzar Pintão ◽  
Momotaro Imaizumi
Keyword(s):  
Intermetallic Compound ◽  
Elastic Properties ◽  
Density Functional ◽  
Minimum Energy ◽  
Young Modulus ◽  
Lattice Parameter ◽  
Full Potential ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Equilibrium Lattice Parameter

The elastic properties of a Ti3Al intermetallic compound were studied using full potential (FP LAPW ) with the APW+lo method. The FP-LAPW is among the most accurate band structure calculations currently available and is based on the density functional theory with general gradient approximation for the exchange and correlation potential. This method provides the structural properties of the ground state as bulk modulus, equilibrium lattice parameter, and equilibrium minimum energy, and the elastic properties as shear modulus, young modulus, Zener coefficient (anisotropy), and Poisson coefficient. The calculated elastic properties are coherent with the elastic properties of the material.

scholarly journals Thyroxine: A Theoretical Study of the Vibrational and Electronic Properties

2020 ◽  
Vol 3 (1) ◽  
pp. 31-40
Author(s):  
Ricardo V. K. Rizzon ◽  
Zélia M. da Costa Ludwig ◽  
Ricardo V. K. Rizzon ◽  
Lucas Modesto da Costa ◽  
Valdemir Ludwig
Keyword(s):  
Density Functional Theory ◽  
Electronic Properties ◽  
Density Functional ◽  
Theoretical Study ◽  
Minimum Energy ◽  
Functional Theory ◽  
Structures And Properties ◽  
The Density Functional Theory ◽  
Infra Red ◽  
Simulation Results

Through this work, we systematically studied the structural, vibrational and electronic properties of the fundamental state of the isolated thyroxine(3,5,3’,5-tetraiodothyronine). The minimum energy structures and properties were obtained using the Density Functional Theory (DFT). Our simulation results were compared with experimental results, including infra-red and Raman spectroscopy with an emphasis on the properties of iodine atoms. The UV-vis spectrum calculated in this work is the first result of this model for the thyroxine molecule.

Estimation of Resonance Energy from Forced Nonplanar Conformations of Conjugated Molecules

2005 ◽  
Vol 70 (10) ◽  
pp. 1577-1588
Author(s):  
Stanislav Böhm ◽  
Otto Exner
Keyword(s):  
Density Functional ◽  
Classical Model ◽  
Minimum Energy ◽  
Resonance Energy ◽  
Isodesmic Reactions ◽  
Conjugated Molecules ◽  
Functional Theory ◽  
Resonance Effects ◽  
The Density Functional Theory ◽  
Derivatives Of

Energies of 39 derivatives of buta-1,3-diene in the twisted conformation were calculated within the framework of the density functional theory at the B3LYP/6-311+G(d,p) level. By comparing with the same molecules in their natural minimum-energy conformations, a scale of resonance effects of various substituents was obtained and expressed in terms of isodesmic reactions. Comparison with other similar scales revealed that this model is not particularly advantageous, its main shortcoming being the relatively small effect. In any case it confirmed that the scales of resonance effects obtained from different models are only very roughly proportional: the classical model of resonance works well in representative examples but has its clear limitation when unduly extended.

scholarly journals Mechanism of the Absorption of CO2 in Ionic Liquid Dimer

2019 ◽  
Vol 45 (1) ◽  
pp. 137-144
Author(s):  
Kalyan Dhar
Keyword(s):  
Ionic Liquid ◽  
Binding Sites ◽  
Density Functional ◽  
Room Temperature ◽  
Minimum Energy ◽  
Co2 Absorption ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Anions And Cations ◽  
Multiple Interactions

The density functional theory (DFT) calculations with the modern continuum solvation model (IEFPCM-SMD) was used to study the mechanism of CO2 absorption at room temperature using ionic liquid such as, [EMIM][BF4] (1-ethyl-3-methylimidazolium tetrafluoroborate) monomer and dimer ionic liquid [IL] dimer comprises two couple of anions and cations, so that more intermolecular interactions are established than in the single IL pair. In this paper, we determined the minimum energy structures and to determine the possible binding sites for CO2 absorption in [EMIM][BF4] monmer and dimer; by comparing the relative minimum energy of [EMIM][BF4] in the presence and in absence of CO2. It was found that CO2 is stabilized by the multiple interactions with several anions. When CO2 penetrates the IL monomer or dimer, through gas-to-liquid diffusion, the O-C-O (CO2)-BF4 intermolecular bond is likely to be formed immediately and bind the CO2 molecule. This result suggests that ionic liquid dimer is suitable for the absorption of CO2. Asiat. Soc. Bangladesh, Sci. 45(1): 137-144, June 2019

scholarly journals Sodium potassium hydrogen citrate, NaKHC6H5O7

2016 ◽  
Vol 72 (2) ◽  
pp. 170-173 ◽  
Author(s):  
Alagappa Rammohan ◽  
James A. Kaduk
Keyword(s):  
Hydrogen Bonds ◽  
Density Functional ◽  
Bond Valence ◽  
Bond Energies ◽  
Functional Theory ◽  
Sodium Potassium ◽  
X Ray ◽  
Potassium Hydrogen ◽  
Bond Valence Sum ◽  
Hydrogen Bond Energies

The crystal structure of sodium potassium hydrogen citrate has been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional theory techniques. The Na+cation is six-coordinate, with a bond-valence sum of 1.17. The K+cation is also six-coordinate, with a bond-valence sum of 1.08. The distorted [NaO6] octahedra share edges, forming chains along theaaxis. The likewise distorted [KO6] octahedra share edges with the [NaO6] octahedra on either side of the chain, and share corners with other [KO6] octahedra, resulting in triple chains along theaaxis. The most prominent feature of the structure is the chain along [111] of very short, very strong hydrogen bonds; the O...O distances are 2.414 and 2.400 Å. The Mulliken overlap populations in these hydrogen bonds are 0.138 and 0.142 e, which correspond to hydrogen-bond energies of 20.3 and 20.6 kcal mol−1.

The Raman Spectra of Nanocomposite Clusters of Atoms in Phosphorous-Selenium Glassy State

2013 ◽  
Vol 667 ◽  
pp. 99-103
Author(s):  
Ahmad Nazrul Rosli ◽  
Hasan Abu Kassim ◽  
Keshav N. Shrivastava ◽  
V. Radhika Devi
Keyword(s):  
Density Functional ◽  
Structural Parameters ◽  
Glassy State ◽  
Minimum Energy ◽  
Vibrational Frequencies ◽  
Self Organization ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Experimental Values ◽  
Large Clusters

We make clusters of atoms of the size of less than 1 nanometer by using the density functional theory and from that we obtain the bond lengths corresponding to the minimum energy configuration. We are able to optimize large clusters of atoms and find the vibrational frequencies for each cluster. This calculation provides us with a method to identify the clusters present in an unknown sample of a glass by comparing the experimental Raman frequency with the calculated value. We start with the experimental values of the Raman frequencies of PSe (Phosphorous-Selenium) glass. We calculate the structural parameters of PSe, P4Se, P2Se2, P4Se5, PSe4, P4Se3 clusters of atoms and tabulate the vibrational frequencies. We compare the calculated values with those measured. In this way we find the clusters of atoms present in the glass. Some times, the same number of atoms can be rearranged in a different symmetry. Hence we learn the symmetries of molecules. We find that certain symmetries are broken due to self-organization in the glassy state.

Structural Shifting and Electronic Properties of Stone-Wales Defect in Armchair Edge (5,5) Carbon Nanotube

2013 ◽  
Vol 772 ◽  
pp. 380-385 ◽  
Author(s):  
Supri Jadi ◽  
A. Setiadi
Keyword(s):  
Carbon Nanotube ◽  
Density Functional ◽  
Minimum Energy ◽  
Elastic Band ◽  
Functional Theory ◽  
Barrier Energy ◽  
Wales Defect ◽  
The Density Functional Theory ◽  
Calculation Results ◽  
Nudge Elastic Band

Stone Wales (SW) defect is one type of topological defect on the CNT, in this study we performed first principles calculations of SW defects in armchair edge (5,5) carbon nanotube (CNT) by the density functional theory (DFT). Two different defects were studied such as longitudinal and circumference types. Our calculation results show that a longitudinal SW defect is more stable than circumference SW defect. However barrier energy as parameter to control the SW defect in CNT was studied, in calculation we applied Nudge Elastic Band (NEB) method to find minimum energy path (MEP) and barrier energy for SW defect transitions. The result shows that barrier energy of circumference SW defect is lower than another one. We also found that in the case of circumference SW defect, armchair edge (5,5) CNT become semiconductor with the band gap of 0.0544 eV.

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