Theoretical study on six-fold coordinated silicon in silicophosphate compounds

2006 ◽  
Vol 84 (8) ◽  
pp. 1024-1030 ◽  
Author(s):  
Hassan Rabaâ ◽  
Fatima Bkiri
Keyword(s):  
Density Functional ◽  
Tight Binding ◽  
High Energy ◽  
Functional Theory ◽  
Model Cluster ◽  
Hartree Fock ◽  
Ir Frequencies ◽  
The Stability ◽  
Remarkable Agreement ◽  
Cluster 2

Extended Hückel tight-binding (EHTB) calculations were performed on silicophosphate compounds with six-coordinated silicon. Speculative structures related to silicon coordination in SiP2O7 are reported. To account for the particular structural distortion caused by the presence of SiO6 in the silicon pyrophosphate, it is important to examine how the stability and the band gap of the extended structure of SiP2O7 are affected. Different theoretical tools are used (EHTB, ab initio Hartree–Fock, and density functional theory DFT-B3LYP). To obtain detailed descriptions of the incorporation of hexacoordinated silicon in this material, the band structures in SiP2O7 and [P2O7]4– were analyzed. It seems that the diffuse orbitals of silicon and the high energy of the Si 3p orbital lead to higher energy coordination and contribute to the breaking of the P-O-P bridge and the forming of a Si-O-P entity in this material. In addition, to provide more evidence of the existence of the octahedral silicon coordination in SiP2O7 (1), two model clusters [P4Si2O23H18] (2) and [P4Si2O19H10] (3) involving silicon atoms in octahedral and tetrahedral sites were investigated using Hartree–Fock and DFT theories. A remarkable agreement between calculated and experimental bond lengths for Si—O and P—O is obtained using the DFT calculation. The model cluster 2 corroborates the structural change in the Si-O-P and P-O-P fragments seen in 1. The IR vibrational frequencies are calculated for both model clusters and are predicted to shift towards lower frequencies in the octahedral Si sites, which is consistent with experimental data.Key words: silicophosphate, SiO6, band structure, tight-binding calculations, Hartree-Fock, DFT, B3LYP, model cluster, IR frequencies.

scholarly journals Density functional tight binding: values of semi-empirical methods in an ab initio era

2014 ◽  
Vol 16 (28) ◽  
pp. 14368-14377 ◽  
Author(s):  
Qiang Cui ◽  
Marcus Elstner
Keyword(s):  
Density Functional Theory ◽  
Ab Initio ◽  
Density Functional ◽  
Tight Binding ◽  
Empirical Methods ◽  
Functional Theory ◽  
Hartree Fock ◽  
Semi Empirical

Semi-empirical (SE) methods are derived from Hartree–Fock (HF) or Density Functional Theory (DFT) by neglect and approximation of electronic integrals.

Computational studies of energetics, electronic structure, and vibrational spectra of PETN nanoparticles

2021 ◽  
Vol 99 (1) ◽  
pp. 63-71
Author(s):  
Qiannan Ma ◽  
Weihua Zhu
Keyword(s):  
Electronic Structure ◽  
Vibrational Spectra ◽  
Density Functional ◽  
Solid Phase ◽  
Tight Binding ◽  
High Energy ◽  
Pentaerythritol Tetranitrate ◽  
Energy Bands ◽  
Extra Energy ◽  
The Stability

The density functional tight binding method was used to explore the energetics, electronic structure, and vibrational spectra of pentaerythritol tetranitrate (PETN) nanoparticles (NPs). The surface energy of the PETN NP is anisotropic and its extra energy decreases with the increase of size. The energy bands of the NPs are significantly expanded and the band gaps are narrowed, thus reducing the stability due to nanometer size effect. The surface of the NP is mainly covered by the NO2 group. The high-energy surface may play a role in triggering chemical decomposition. The vibration frequencies of the PETN NPs present a wider distribution than those of the gas and solid phase PETN, which will increase the probability of energy transfer to the molecules in the system and promote the decomposition of PETN. Our results provide a basic understanding from a molecular perspective to the energy properties of nano explosives.

scholarly journals Vibrational Spectroscopic Study of (E)-4-(Benzylideneamino)-N-Carbamimidoyl Benzenesulfonamide

2012 ◽  
Vol 2012 ◽  
pp. 1-11 ◽  
Author(s):  
Asha Chandran ◽  
Sheena Mary ◽  
Hema Tresa Varghese ◽  
C. Yohannan Panicker ◽  
T. K. Manojkumar ◽  
...  
Keyword(s):  
Fourier Transform ◽  
Potential Energy ◽  
Density Functional ◽  
Potential Energy Distribution ◽  
Geometrical Parameters ◽  
Functional Theory ◽  
Hartree Fock ◽  
The Fourier Transform ◽  
The Stability ◽  
Surface Scan

The Fourier transform infrared and Fourier transform Raman spectra of (E)-4-(benzylideneamino)-N-carbamimidoyl benzenesulfonamide were recorded and analyzed. Geometry and harmonic vibrational wavenumbers were calculated theoretically using Gaussian 03 set of quantum chemistry codes. Calculations were performed at the Hartree-Fock (HF) and density functional theory (DFT; B3PW91, B3LYP) levels of theory. The calculated wavenumbers (B3LYP) agree well with the observed wavenumbers. Potential energy distribution is done using GAR2PED program. The red shift of the N-H stretching band in the infrared spectrum from the computed wavenumber indicates the weakening of the N-H bond. The geometrical parameters of the title compound are in agreement with that of reported similar derivatives. The calculated first hyperpolarizability is comparable with the reported value of similar derivative and may be an attractive object for further studies of nonlinear optics. Potential energy surface scan studies have been carried out to understand the stability of planar and nonplanar structures of the molecule.

Comparative theoretical synthesis of high-energy explosive 1,4,5,8-tetranitro-1,4,5,8-tetraazadecalin

2014 ◽  
Vol 13 (05) ◽  
pp. 1450045 ◽  
Author(s):  
Ken-Fa Cheng ◽  
Min-Hsien Liu
Keyword(s):  
Density Functional ◽  
Raw Materials ◽  
Condensation Reaction ◽  
High Energy ◽  
Reaction Scheme ◽  
Base Function ◽  
Functional Theory ◽  
Compound A ◽  
Hartree Fock ◽  
Theoretical Synthesis

Reaction mechanisms were proposed in this study for the theoretical synthesis of high-energy 1,4,5,8-tetranitro-1,4,5,8-tetraazadecalin (TNAD). Corresponding computations were performed using density functional theory (DFT) and the Hartree Fock (HF) method with the same 6-31G(d,p) base function. Glyoxal and ethylenediamine were used as the raw materials and were placed into respective gaseous and solvated (water or ethanol) environments to proceed the condensation reaction to form the precursor 1,4,5,8-tetraazadecalin, which subsequently underwent four stages of nitro-group substitution to obtain the target TNAD compound. A whole reaction scheme closely related to the experimental processes was successfully constructed, and the corresponding energy barriers were estimated for each elementary reaction. The findings revealed that the overall activation energy by B3LYP/6-31G(d,p) calculation is 2660.4 kJ/mol, which is lower than the 2832.1 kJ/mol calculated by HF/6-31G(d,p) computation. Furthermore, the reaction has a lower overall energy barrier in the solvated environment than in the gaseous system, being 2389.6 kJ/mol in ethanol, 2428.7 kJ/mol in water and 2660.4 kJ/mol in the gaseous phase. The ethanol-solvated system is suggested to be the most suitable medium for the synthesis of TNAD.

scholarly journals Crystalline Peroxosolvates: Nature of the Coformer, Hydrogen-Bonded Networks and Clusters, Intermolecular Interactions

Molecules ◽  
2020 ◽  
Vol 26 (1) ◽  
pp. 26
Author(s):  
Alexander G. Medvedev ◽  
Andrei V. Churakov ◽  
Petr V. Prikhodchenko ◽  
Ovadia Lev ◽  
Mikhail V. Vener
Keyword(s):  
Density Functional ◽  
High Energy ◽  
Proton Donor ◽  
Proton Acceptor ◽  
Functional Theory ◽  
Sodium Percarbonate ◽  
Analgesic Effects ◽  
1D Chain ◽  
The Stability ◽  
Insight Into

Despite the technological importance of urea perhydrate (percarbamide) and sodium percarbonate, and the growing technological attention to solid forms of peroxide, fewer than 45 peroxosolvates were known by 2000. However, recent advances in X-ray diffractometers more than tripled the number of structurally characterized peroxosolvates over the last 20 years, and even more so, allowed energetic interpretation and gleaning deeper insight into peroxosolvate stability. To date, 134 crystalline peroxosolvates have been structurally resolved providing sufficient insight to justify a first review article on the subject. In the first chapter of the review, a comprehensive analysis of the structural databases is carried out revealing the nature of the co-former in crystalline peroxosolvates. In the majority of cases, the coformers can be classified into three groups: (1) salts of inorganic and carboxylic acids; (2) amino acids, peptides, and related zwitterions; and (3) molecular compounds with a lone electron pair on nitrogen and/or oxygen atoms. The second chapter of the review is devoted to H-bonding in peroxosolvates. The database search and energy statistics revealed the importance of intermolecular hydrogen bonds (H-bonds) which play a structure-directing role in the considered crystals. H2O2 always forms two H-bonds as a proton donor, the energy of which is higher than the energy of analogous H-bonds existing in isostructural crystalline hydrates. This phenomenon is due to the higher acidity of H2O2 compared to water and the conformational mobility of H2O2. The dihedral angle H-O-O-H varies from 20 to 180° in crystalline peroxosolvates. As a result, infinite H-bonded 1D chain clusters are formed, consisting of H2O2 molecules, H2O2 and water molecules, and H2O2 and halogen anions. H2O2 can form up to four H-bonds as a proton acceptor. The third chapter of the review is devoted to energetic computations and in particular density functional theory with periodic boundary conditions. The approaches are considered in detail, allowing one to obtain the H-bond energies in crystals. DFT computations provide deeper insight into the stability of peroxosolvates and explain why percarbamide and sodium percarbonate are stable to H2O2/H2O isomorphic transformations. The review ends with a description of the main modern trends in the synthesis of crystalline peroxosolvates, in particular, the production of peroxosolvates of high-energy compounds and mixed pharmaceutical forms with antiseptic and analgesic effects.

scholarly journals Computational Investigation and Screening of High-Energy-Density Materials: Based on Nitrogen-Rich 1,2,4,5-tetrazine Energetic Derivatives

2021 ◽  
Author(s):  
Lian Zeng ◽  
Yuhe Jiang ◽  
Jinting Wu ◽  
Hongbo Li ◽  
Jianguo Zhang
Keyword(s):  
Enthalpy Of Formation ◽  
Density Functional ◽  
High Energy ◽  
High Energy Density ◽  
Detonation Performance ◽  
Detonation Properties ◽  
Functional Theory ◽  
High Energy Density Materials ◽  
The Stability ◽  
The Enthalpy Of Formation

Abstract: In the present work, the geometric structures, the frontier molecular orbitals and the enthalpy of formation (HOF) of thirty six 1, 2, 4, 5-tetrazine derivatives (FTT) were systematically studied by using the B3LYP/6-311+G* method of density functional theory. Meanwhile, we also predicted the stability, detonation properties and thermodynamic properties of all FTT compounds. Results showed that all compounds have superior enthalpy of formation far exceeding that of common explosives RDX and HMX, ranging from 859kJ·mol-1-1532kJ·mol-1. In addition, the detonation performance (Q = 1426cal·g-1 -1804cal·g-1; P = 29.54GPa - 41.84GPa; D = 8.02km·s-1 - 9.53km·s-1), which is superior to TATB and TNT. It is also concluded that the introduction of coordination oxygen on the tetrazine ring can improve the HOF, density and detonation performance of the title compound, and -NH-NH- bridge and -NHNO2 group are also the perfect combination to increase these values. In view of stability, because of the fascinating performance of D3 (ρ =1.89g·cm-3; D = 9.38km·s-1; P = 40.13GPa)，E3(ρ = 1.87g·cm-3; D = 9.19km·s-1; P = 38.35GPa), F1 (ρ = 1.87g·cm-3; D = 9.42km·s-1; P = 40.23GPa) and F3 (ρ= 1.92g·cm-3; D = 9.53km·s-1; P = 41.84GPa), makes them very attractive to be chosen as HEDMs.

Thermodynamic Stability of Hexagonal and Rhombohedral Bn at Cvd Conditions from Van der Waals Corrected First Principles Calculations

2019 ◽  
Author(s):  
Henrik Pedersen ◽  
Björn Alling ◽  
Hans Högberg ◽  
Annop Ektarawong
Keyword(s):  
Thin Films ◽  
Thermodynamic Stability ◽  
First Principles ◽  
Thermal Equilibrium ◽  
Density Functional ◽  
Van Der Waals ◽  
Chemical Vapor ◽  
First Principles Calculations ◽  
Functional Theory ◽  
The Stability

Thin films of boron nitride (BN), particularly the sp<sup>2</sup>-hybridized polytypes hexagonal BN (h-BN) and rhombohedral BN (r-BN) are interesting for several electronic applications given band gaps in the UV. They are typically deposited close to thermal equilibrium by chemical vapor deposition (CVD) at temperatures and pressures in the regions 1400-1800 K and 1000-10000 Pa, respectively. In this letter, we use van der Waals corrected density functional theory and thermodynamic stability calculations to determine the stability of r-BN and compare it to that of h-BN as well as to cubic BN and wurtzitic BN. We find that r-BN is the stable sp<sup>2</sup>-hybridized phase at CVD conditions, while h-BN is metastable. Thus, our calculations suggest that thin films of h-BN must be deposited far from thermal equilibrium.

Site preference and atomic ordering in the ternary Rh5Ga2As: first-principles calculations

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Nilanjan Roy ◽  
Sucharita Giri ◽  
Harshit ◽  
Partha P. Jana
Keyword(s):  
Total Energy ◽  
First Principles ◽  
Density Functional ◽  
Structure Type ◽  
Site Preference ◽  
X Ray Diffraction ◽  
Atomic Ordering ◽  
Functional Theory ◽  
The Stability ◽  
Bonding Characteristics

Abstract The site preference and atomic ordering of the ternary Rh5Ga2As have been investigated using first-principles density functional theory (DFT). An interesting atomic ordering of two neighboring elements Ga and As reported in the structure of Rh5Ga2As by X-ray diffraction data only is confirmed by first-principles total-energy calculations. The previously reported experimental model with Ga/As ordering is indeed the most stable in the structure of Rh5Ga2As. The calculation detected that there is an obvious trend concerning the influence of the heteroatomic Rh–Ga/As contacts on the calculated total energy. Interestingly, the orderly distribution of As and Ga that is found in the binary GaAs (Zinc-blende structure type), retained to ternary Rh5Ga2As. The density of states (DOS) and Crystal Orbital Hamiltonian Population (COHP) are calculated to enlighten the stability and bonding characteristics in the structure of Rh5Ga2As. The bonding analysis also confirms that Rh–Ga/As short contacts are the major driving force towards the overall stability of the compound.

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