A new carbon allotrope with orthorhombic symmetry formed via graphitic sheet buckling

2018 ◽  
Vol 20 (35) ◽  
pp. 22762-22767 ◽  
Author(s):  
Zhen-Zhen Li ◽  
Jian-Tao Wang
Keyword(s):  
Ab Initio ◽  
Unit Cell ◽  
Orthorhombic Symmetry ◽  
Covalent Bonds ◽  
Carbon Allotrope ◽  
Graphitic Sheet

We identified by ab initio calculations a new simple orthorhombic carbon allotrope with Pmc21 (C2v2) symmetry that has a 32-atom unit cell in all-sp3 hybridized covalent bonds.

Electronic Structure of Defects in Fcc-C22

2006 ◽  
Vol 965 ◽  
Author(s):  
Helder Sousa Domingos
Keyword(s):  
Electronic Structure ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Spin Polarization ◽  
Dopant Concentration ◽  
Magnetic Polarization ◽  
Carbon Allotrope

ABSTRACTClassical and ab-initio calculations were carried out on bulk defects and surfaces of the carbon allotrope Fcc-C22. The results revealed a number of possible defects with spin polarization and one with antiferromagnetic character. The surfaces were shown to be able to host magnetic polarization. Extrinsic light dopants (H and N) were shown to introduce spin polarization for small dopant concentration and to metallize the systems for large concentrations.

scholarly journals Non-Covalent Interactions Involving Alkaline-Earth Atoms and Lewis Bases B: An ab Initio Investigation of Beryllium and Magnesium Bonds, B···MR2 (M = Be or Mg, and R = H, F or CH3)

Inorganics ◽  
2019 ◽  
Vol 7 (3) ◽  
pp. 35 ◽  
Author(s):  
Ibon Alkorta ◽  
Anthony Legon
Keyword(s):  
Ab Initio ◽  
Lewis Acids ◽  
Alkaline Earth ◽  
Basis Set ◽  
Covalent Bonds ◽  
Lewis Bases ◽  
Complete Basis Set ◽  
Definition Of ◽  
The Individual ◽  
Equilibrium Dissociation

Geometries, equilibrium dissociation energies (De), intermolecular stretching, and quadratic force constants (kσ) determined by ab initio calculations conducted at the CCSD(T)/aug-cc-pVTZ level of theory, with De obtained by using the complete basis set (CBS) extrapolation [CCSD(T)/CBS energy], are presented for the B···BeR2 and B···MgR2 complexes, where B is one of the following Lewis bases: CO, H2S, PH3, HCN, H2O or NH3, and R is H, F or CH3. The BeR2 and MgR2 precursor molecules were shown to be linear and non-dipolar. The non-covalent intermolecular bond in the B···BeR2 complexes is shown to result from the interaction of the electrophilic band around the Be atom of BeR2 (as indicated by the molecular electrostatic potential surface) with non-bonding electron pairs of the base, B, and may be described as a beryllium bond by analogy with complexes such as B···CO2, which contain a tetrel bond. The conclusions for the B···MgR2 series are similar and a magnesium bond can be correspondingly invoked. The geometries established for B···BeR2 and B···MgR2 can be rationalized by a simple rule previously enunciated for tetrel-bonded complexes of the type B···CO2. It is also shown that the dissociation energy, De, is directly proportional to the force constant, kσ, in each B···MR2 series, but with a constant of proportionality different from that established for many hydrogen-bonded B···HX complexes and halogen-bonded B···XY complexes. The values of the electrophilicity, EA, determined from the De for B···BeR2 complexes for the individual Lewis acids, A, reveal the order A = BeF2 > BeH2 > Be(CH3)2—a result that is consistent with the −I and +I effects of F and CH3 relative to H. The conclusions for the MgR2 series are similar but, for a given R, they have smaller electrophilicities than those of the BeR2 series. A definition of alkaline-earth non-covalent bonds is presented.

scholarly journals ab initio Structural, Electronic and Vibrational Properties of GaSb Nanocrystals Using Diamondoids and Large Unit Cell Method

2015 ◽  
Vol 27 (6) ◽  
pp. 2200-2204
Author(s):  
Mudar Ahmed Abdulsattar ◽  
Majed M. Mohamad
Keyword(s):  
Ab Initio ◽  
Unit Cell ◽  
Vibrational Properties ◽  
Large Unit ◽  
Cell Method ◽  
Large Unit Cell

scholarly journals Bulachite, [Al6(AsO4)3(OH)9(H2O)4]⋅2H2O from Cap Garonne, France: Crystal structure and formation from a higher hydrate

2020 ◽  
Vol 84 (4) ◽  
pp. 608-615
Author(s):  
Ian E. Grey ◽  
Emre Yoruk ◽  
Stéphanie Kodjikian ◽  
Holger Klein ◽  
Catherine Bougerol ◽  
...  
Keyword(s):  
Unit Cell ◽  
Orthorhombic Symmetry ◽  
X Ray Diffraction ◽  
Unit Cell Parameters ◽  
Space Group ◽  
X Ray ◽  
Cell Parameters ◽  
Different Temperatures ◽  
Using Data ◽  
Hydrated Aluminium

AbstractBulachite specimens from Cap Garonne, France, comprise two intimately mixed hydrated aluminium arsenate minerals with the same Al:As ratio of 2:1 and with different water contents. The crystal structures of both minerals have been solved using data from low-dose electron diffraction tomography combined with synchrotron powder X-ray diffraction. One of the minerals has the same powder X-ray diffraction pattern (PXRD) as for published bulachite. It has orthorhombic symmetry, space group Pnma with unit-cell parameters a = 15.3994(3), b = 17.6598(3), c = 7.8083(1) Å and Z = 4, with the formula [Al6(AsO4)3(OH)9(H2O)4]⋅2H2O. The second mineral is a higher hydrate with composition [Al6(AsO4)3(OH)9(H2O)4]⋅8H2O. It has the same Pnma space group and unit-cell parameters a = 19.855(4), b = 17.6933(11) and c = 7.7799(5) Å i.e. almost the same b and c parameters but a much larger a parameter. The structures are based on polyhedral layers, parallel to (100), of composition [Al6(AsO4)3(OH)9(H2O)4] and with H-bonded H2O between the layers. The layers contain [001] spiral chains of edge-shared octahedra, decorated with corner connected AsO4 tetrahedra that are the same as in the mineral liskeardite. The spiral chains are joined together by octahedral edge-sharing to form layers parallel to (100). Synchrotron PXRD patterns collected at different temperatures during heating of the specimen show that the higher-hydrate mineral starts transforming to bulachite when heated to 50°C, and the transformation is complete between 75 and 100°C.

scholarly journals Simulation of Electronic Structure of Aluminum Phosphide Nanocrystals Using Ab Initio Large Unit Cell Method

2012 ◽  
Vol 2012 ◽  
pp. 1-6 ◽  
Author(s):  
Hamad R. Jappor ◽  
Zeyad Adnan Saleh ◽  
Mudar A. Abdulsattar
Keyword(s):  
Electronic Structure ◽  
Ab Initio ◽  
Unit Cell ◽  
Aluminum Phosphide ◽  
Large Unit ◽  
Cell Method ◽  
Large Unit Cell

Uniqueness of the macromolecular crystallographic phase problem

2015 ◽  
Vol 71 (6) ◽  
pp. 592-598 ◽  
Author(s):  
Rick P. Millane ◽  
Romain D. Arnal
Keyword(s):  
Ab Initio ◽  
Single Particle ◽  
Real Space ◽  
Unit Cell ◽  
Macromolecular Crystallography ◽  
Phase Problem ◽  
Particle Imaging ◽  
Single Particle Imaging ◽  
Molecular Envelope ◽  
Constraint Ratio

Uniqueness of the phase problem in macromolecular crystallography, and its relationship to the case of single particle imaging, is considered. The crystallographic problem is characterized by a constraint ratio that depends only on the size and symmetry of the molecule and the unit cell. The results are used to evaluate the effect of various real-space constraints. The case of an unknown molecular envelope is considered in detail. The results indicate the quite wide circumstances under whichab initiophasing should be possible.

scholarly journals Electronic Structure of Hydrogenated and Surface-Modified GaAs Nanocrystals: Ab Initio Calculations

2012 ◽  
Vol 2012 ◽  
pp. 1-5 ◽  
Author(s):  
Hamsa Naji Nasir ◽  
Mudar A. Abdulsattar ◽  
Hayder M. Abduljalil
Keyword(s):  
Electronic Structure ◽  
Ab Initio ◽  
Valence Band ◽  
Density Functional ◽  
Energy Gap ◽  
Unit Cell ◽  
Large Unit ◽  
Geometrical Optimization ◽  
Large Unit Cell ◽  
Core Part

Two methods are used to simulate electronic structure of gallium arsenide nanocrystals. The cluster full geometrical optimization procedure which is suitable for small nanocrystals and large unit cell that simulates specific parts of larger nanocrystals preferably core part as in the present work. Because of symmetry consideration, large unit cells can reach sizes that are beyond the capabilities of first method. The two methods use ab initio Hartree-Fock and density functional theory, respectively. The results show that both energy gap and lattice constant decrease in their value as the nanocrystals grow in size. The inclusion of surface part in the first method makes valence band width wider than in large unit cell method that simulates the core part only. This is attributed to the broken symmetry and surface passivating atoms that split surface degenerate states and adds new levels inside and around the valence band. Bond length and tetrahedral angle result from full geometrical optimization indicate good convergence to the ideal zincblende structure at the centre of hydrogenated nanocrystal. This convergence supports large unit cell methodology. Existence of oxygen atoms at nanocrystal surface melts down density of states and reduces energy gap.

scholarly journals An ab initio investigation of alkali–metal non-covalent bonds B⋯LiR and B⋯NaR (R = F, H or CH3) formed with simple Lewis bases B: the relative inductive effects of F, H and CH3

2020 ◽  
Vol 22 (28) ◽  
pp. 16421-16430 ◽  
Author(s):  
Ibon Alkorta ◽  
J. Grant Hill ◽  
Anthony C. Legon
Keyword(s):  
Alkali Metal ◽  
Ab Initio ◽  
Covalent Bonds ◽  
Lewis Bases ◽  
Inductive Effects ◽  
Non Covalent Interactions ◽  
Metal Bonds ◽  
Covalent Interactions

Alkali–metal bonds formed by LiR and NaR (R = F, H, CH3) with each of the Lewis bases OC, HCN, H2O, H3N, H2S and H3P are investigated ab initio at the CCSD(T)/AVTZ and CCSD(T)/awCVTZ levels to characterise these non-covalent interactions.

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