Momentum space properties of various orbital basis sets used in quantum chemical calculations

1982 ◽  
Vol 21 (2) ◽  
pp. 419-429 ◽  
Author(s):  
Alfredo M. Simas ◽  
Art J. Thakkar ◽  
Vedene H. Smith
Keyword(s):  
Quantum Chemical Calculations ◽  
Momentum Space ◽  
Quantum Chemical ◽  
Basis Sets ◽  
Orbital Basis

Complexes of SiH\(_2^{2+}\) with Carbodiphosphorane and Analogues {E(PPh\(_3\))\(_2\)} (E = C – Pb) in Unusual Bonding Mode

2014 ◽  
Vol 23 (4) ◽  
Author(s):  
Tat Van Pham
Keyword(s):  
Quantum Chemical Calculations ◽  
Quantum Chemical ◽  
Significant Contribution ◽  
Phenyl Group ◽  
Basis Sets ◽  
Group 14 ◽  
Bonding Analysis ◽  
Equilibrium Geometries ◽  
Bonding Mode

Quantum chemical calculations at the BP86 level with various basis sets (SVP, TZVPP) were carried out for complexes of carbodiphosphorane analogues E(PPh3)2 with E = C–Pb. The equilibrium geometries of the complexes [SiH22+–{E(PPh3)2}] (Si2+-1E) possess the carbodiphosphorane ligand 1C is slightly bonded in a tilted way to SiH22+ in the complex Si2+-1C, whereas the heavier group-14 ligands E(PPh3)2 (E = Si – Pb) in the complexes Si2+-1Si – Si2+-1Pb are strongly bonded in side-on fashions. The surprising structures SiH22+-tetrylone complexes possess a strong Si-C1 bond between the Si atom of the SiH22+ fragment and atom C1 of the phenyl group. The trend of the BDEs for the Si-E bond in the Si2+-1E complexes is Si2+-1C ~ Si2+-1Si < Si2+-1Ge < Si2+-1Sn < Si2+-1Pb. Bonding analysis of the complexes shows that the Si-E bonds have a significant contribution from H2Si2+←E(PPh3)2 π-donation.

Thiadiazole-2-Thiol-5-Thione and 2,5-Dimercapto-1,3,4-Thiadiazol Tautomerism, Conformational Stability, Vibrational Assignments, Inhibitor Efficiency and Quantum Chemical Calculations

2020 ◽  
Vol 234 (3) ◽  
pp. 415-440 ◽  
Author(s):  
Muhammad H. Esmaiel ◽  
Hany A. Basuony ◽  
Mohamed K. Al-Nawasany ◽  
Musab M. Shulkamy ◽  
Ibrahim A. Shaaban ◽  
...  
Keyword(s):  
Solid State ◽  
Potential Energy ◽  
Quantum Chemical Calculations ◽  
Quantum Chemical ◽  
Density Functional ◽  
Solid Phase ◽  
Thiol Group ◽  
Basis Set ◽  
Basis Sets ◽  
Vibrational Assignments

AbstractRaman (3700–100 cm−1) and infrared (4000–400 cm−1) spectra of 2,5-Dimercapto-1,3,4-thiadiazol (DMTD) were recorded in the solid phase. Six structures (1–6) were initially proposed for DMTD as a result of thiol-thione tautomerism and internal rotation(s) of thiol group(s) around the C–S bond. Quantum chemical calculations were carried out for an isolated molecule (1–6) using density functional theory (B3LYP) and ab initio MP2(full) methods utilizing 6-31G(d) and 6-311++G(d,p) basis sets which favor thiol-thione tautomerism (structure 4). Relaxed potential energy surface scans of structure 4 revealed an additional conformer (the thiol group is out-of-plane, structure 7) using the aforementioned methods at 6-311++G(d,p) basis set. For additional verification, plane-wave solid state calculations were carried out at PW91 and PBEsol came out in favor of conformer 7. This is in agreement with the computed/observed SH in-plane bending of S-7 (959/941 cm−1) rather than the one estimated at (880 cm−1) for S-4. Moreover, the observed split IR/Raman bands were found consistent with solid state calculated frequencies of S-7 assuming two molecules per unit cell bonded via H-bonding intermolecular interactions. Aided by vibrational frequency calculations, normal coordinate analysis, force constants and potential energy distributions (PEDs), a complete vibrational assignment for the observed IR and Raman bands is proposed herein. Furthermore, we have estimated the frontier molecular orbitals and atomic charges to account for the corrosion inhibition efficiency of DMTD along with its binding sites to the metal surface. Our results are discussed herein and compared to similar molecules whenever appropriate.

Dative versus electron-sharing bonding in N-oxides and phosphane oxides R3EO and relative energies of the R2EOR isomers (E = N, P; R = H, F, Cl, Me, Ph). A theoretical study

2018 ◽  
Vol 20 (17) ◽  
pp. 11856-11866 ◽  
Author(s):  
Tao Yang ◽  
Diego M. Andrada ◽  
Gernot Frenking
Keyword(s):  
Density Functional Theory ◽  
Ab Initio ◽  
Quantum Chemical Calculations ◽  
Quantum Chemical ◽  
Density Functional ◽  
Theoretical Study ◽  
Basis Sets ◽  
Functional Theory

Quantum chemical calculations using ab initio methods at the CCSD(T)/def2-TZVPP level and density functional theory using BP86 and M06-2X functionals in conjunction with def2-TZVPP basis sets have been carried out on the title molecules.

DFT and Bader's AIM analysis of 2,5-,diphenyl-1,3,4-oxadizole molecule: A organic light emitting diode (OLED)

2015 ◽  
Vol 14 (05) ◽  
pp. 1550038 ◽  
Author(s):  
P. Srinivasan ◽  
A. David Stephen
Keyword(s):  
Electron Density ◽  
Quantum Chemical Calculations ◽  
Quantum Chemical ◽  
Density Functional ◽  
Light Emitting Diode ◽  
Basis Sets ◽  
Bond Critical Point ◽  
Light Emitting ◽  
Organic Light Emitting Diode ◽  
Organic Light

The electron density and conductivity studies of 2,5-diphenyl-1,3,4-oxadizole organic light emitting diode (OLED) based molecule have been calculated from the quantum chemical calculations and combined with the Bader's AIM theory. Density functional theory calculations with B3LYP/aug-cc-PVDZ basis sets was used to determine ground state gas space molecular geometries (bond lengths and bond angles), electron density and bonding features of this molecule. The electron densities at the bond critical point (BCP) of aromatic Car–Car bonds are much stronger than the other bonds in the molecule. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. The HOMO–LUMO gap calculated from quantum chemical calculations has been compared with the value calculated from the density of states. The negative electrostatic potential (ESP) is concentrated solely around the N atoms, whereas in the rest of the region a positive ESP to dominate.

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