Accurate modeling of molecular crystal through dispersion-corrected density functional theory (DFT-D) method

2011 ◽  
Vol 1301 ◽  
Author(s):  
Bohdan Schatschneider ◽  
Jian-jie Liang
Keyword(s):  
Density Functional Theory ◽  
Phase Transformation ◽  
Density Functional ◽  
Pressure Response ◽  
Van Der Waals Interactions ◽  
Group Symmetry ◽  
Functional Theory ◽  
Space Group Symmetry ◽  
Space Group ◽  
Structural Details

ABSTRACTCrystal structure, pressure response, and polymorph transformation were investigated for crystalline indole through dispersion-corrected density functional theory (DFT-D) method. An accurate, nonempirical method (as in the latest implementations of CASTEP) is used to correct for the general DFT scheme to include van der Waals interactions important in molecular crystals. Ambient structural details, including space group symmetry, density, and fine structural details, such as bicyclic angles, have been reproduced to within experimental accuracy. Pressure response of the structure was obtained to isostatic pressure up to 25 GPa, in increments of 1 GPa. Evolution of space group symmetry and the bicyclic angle were mapped as a function of pressure. A previously unknown phase transformation has been identified around 14 GPa of isostatic pressure. Total energies of the phases before and after phase transformation are nearly identical, with a phase transformation barrier of 0.9 eV. The study opens up the door to reliable DFT investigations of chemical reactions of crystalline aromatic systems under high pressure (e.g. formation of amorphous sp3 hybridized phases).

Validation of missed space-group symmetry in X-ray powder diffraction structures with dispersion-corrected density functional theory

2017 ◽  
Vol 73 (4) ◽  
pp. 756-766 ◽  
Author(s):  
Daniela Hempler ◽  
Martin U. Schmidt ◽  
Jacco van de Streek
Keyword(s):  
Density Functional Theory ◽  
Crystal Structures ◽  
Powder Diffraction ◽  
Energy Minimization ◽  
Molecular Crystal ◽  
Density Functional ◽  
Group Symmetry ◽  
Functional Theory ◽  
Space Group Symmetry ◽  
Space Group

More than 600 molecular crystal structures with correct, incorrect and uncertain space-group symmetry were energy-minimized with dispersion-corrected density functional theory (DFT-D, PBE-D3). For the purpose of determining the correct space-group symmetry the required tolerance on the atomic coordinates of all non-H atoms is established to be 0.2 Å. For 98.5% of 200 molecular crystal structures published with missed symmetry, the correct space group is identified; there are no false positives. Very small, very symmetrical molecules can end up in artificially high space groups upon energy minimization, although this is easily detected through visual inspection. If the space group of a crystal structure determined from powder diffraction data is ambiguous, energy minimization with DFT-D provides a fast and reliable method to select the correct space group.

scholarly journals Density functional theory study of electronic properties of Bi2Se3 and Bi2Te3

2017 ◽  
Vol 12 (3) ◽  
Author(s):  
Abdullahi Lawal ◽  
Amiruddin Shaari
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Topological Insulators ◽  
Van Der Waals Interactions ◽  
Partial Density ◽  
Total Density ◽  
Density Of State ◽  
Generalized Gradient ◽  
Linear Dispersion ◽  
Functional Theory

Topological insulators are layered materials via van der Waals interactions with hexagonal unit cell similar to that of graphene. The exciting features of Bi2Se3 and Bi2Te3 topological insulators their zero band gap surface states exhibiting linear dispersion at the Fermi energy. We present here first principles study pertaining to electronics properties of Bi2Se3 and Bi2Te3 compound with and without spin-orbit interaction using density functional theory (DFT). Total density of state (DOS), partial density of state (PDOS) and band structure where determined by Quantum-Espresso simulation package which uses plane wave basis and pseudopotential for the core electrons, while treating exchange-correlation potential with generalized gradient approximation (GGA). From our computations, the obtained results were found to be consistent with the available experimental results. 

scholarly journals Synthesis, Characterization, and Crystal Structure Determination of a New Lithium Zinc Iodate Polymorph LiZn(IO3)3

Crystals ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 464 ◽  
Author(s):  
Hebboul ◽  
Galez ◽  
Benbertal ◽  
Beauquis ◽  
Mugnier ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Density Functional Theory ◽  
Density Functional ◽  
Second Harmonic ◽  
Infrared Absorption Spectrum ◽  
Density Functional Theory Calculations ◽  
Functional Theory ◽  
Space Group ◽  
X Ray ◽  
Cell Parameters

Synthesis and characterization of anhydrous LiZn(IO3)3 powders prepared from an aqueous solution are reported. Morphological and compositional analyses were carried out by using scanning electron microscopy and energy-dispersive X-ray measurements. The synthesized powders exhibited a needle-like morphology after annealing at 400 °C. A crystal structure for the synthesized compound was proposed from powder X-ray diffraction and density-functional theory calculations. Rietveld refinements led to a monoclinic structure, which can be described with space group P21, number 4, and unit-cell parameters a = 21.874(9) Å, b = 5.171(2) Å, c = 5.433(2) Å, and  = 120.93(4)°. Density-functional theory calculations supported the same crystal structure. Infrared spectra were also collected, and the vibrations associated with the different modes were discussed. The non-centrosymmetric space group determined for this new polymorph of LiZn(IO3)3, the characteristics of its infrared absorption spectrum, and the observed second-harmonic generation suggest it is a promising infrared non-linear optical material.

scholarly journals Structure and Symmetrization of Hydrogen Bonding in Ices VIII and X at High Pressure: A Density Functional Theory Approach

2015 ◽  
Vol 19 (2) ◽  
pp. 14-18
Author(s):  
Nurapati Pantha ◽  
Narayan Prasad Adhikari
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Science And Technology ◽  
Group Symmetry ◽  
Initial Structure ◽  
Theory Approach ◽  
Functional Theory ◽  
Cell Parameters ◽  
Transition Pressure ◽  
Experimental Values

We study the change in structural properties of ice by taking initial structure of “ice VIII”, with space group symmetry I41/amd, as a function of elevating pressure up to 120 GPa in density-functional theory (DFT) level of calculations implemented by Quantum ESPRESSO package. Consistent with the standard laws of thermodynamics, our calculations show that the physical size (volume and cell parameters) of the unit cell compresses monotonically on increasing pressure. We also compare our DFT results of these parameters with the available experimental values performed at finite temperature. The comparison shows good agreement between the quantities, within 5%, with slightly higher experimental values. At 100 GPa of pressure, hydrogen atom comes exactly at the midpoint of two boneded oxygens, called hydrogen-bonded symmetrization, which at low pressure remains nearby one of the oxygens. This symmmetrized structure is characterized by a new phase of the system known as “ice X” and the boundary pressure, 100 GPa, defines the transition pressure (P0) for changing phase from “ice VIII” to “ice X”. The transition pressure (P0) of the present work agrees well within 2% of previously reported results.Journal of Institute of Science and Technology, 2014, 19(2): 14-19Journal of Institute of Science and Technology, 2014, 19(2): 14-18

ADSORPTION OF THIOPHENE ON N-DOPED TiO2/MoS2 NANOCOMPOSITES INVESTIGATED BY VAN DER WAALS CORRECTED DENSITY FUNCTIONAL THEORY

2018 ◽  
Vol 25 (01) ◽  
pp. 1850038
Author(s):  
AMIRALI ABBASI ◽  
JABER JAHANBIN SARDROODI
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Van Der Waals ◽  
Titanium Atom ◽  
Density Functional Theory Calculations ◽  
Van Der Waals Interactions ◽  
Functional Theory ◽  
Structural And Electronic Properties ◽  
Potential Applicability ◽  
Thiophene Molecule

Comparison of structural and electronic properties between pristine and N-doped titanium dioxide-(TiO2)/molybdenum disulfide (MoS2) nanocomposites and their effects on the adsorption of thiophene molecule were performed using density functional theory calculations. To correctly estimate the adsorption energies, the van der Waals interactions were taken into account in the calculations. On the TiO2/MoS2 nanocomposite, thiophene molecule tends to be strongly adsorbed by its sulfur atom. The five-fold coordinated titanium atom of TiO2 was found to be an active binding site for thiophene adsorption. The results suggest that the thiophene molecule has not any mutual interaction with MoS2 nanosheet. The electronic structures of the complex systems are discussed in terms of the density of states and molecular orbitals of the thiophene molecules adsorbed to the TiO2/MoS2 nanocomposites. It was also found that the doping of nitrogen atom is conductive to the interaction of thiophene with nanocomposite. Thus, it can be concluded that the interaction of thiophene with N-doped TiO2/MoS2 nanocomposite is more energetically favorable than the interaction with undoped nanocomposite. The sensing capability of TiO2/MoS2 toward thiophene detection was greatly increased upon nitrogen doping. These processes ultimately lead to the strong adsorption of thiophene on the N-doped TiO2/MoS2 nanocomposites, indicating potential applicability of these nanocomposites as novel gas sensors.

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