Accurate quadruple-ζ basis-set approximation for double-hybrid density functional theory with an order of magnitude reduction in computational cost

2013 ◽  
Vol 133 (2) ◽  
Author(s):  
Bun Chan ◽  
Leo Radom
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Computational Cost ◽  
Basis Set ◽  
Hybrid Density Functional Theory ◽  
Functional Theory ◽  
Order Of Magnitude ◽  
Set Approximation ◽  
Hybrid Density Functional

Complete basis set, hybrid-density functional theory study, and natural bond orbital interpretations of the conformational behavior of halocarbonyl, thiocarbonyl, and selenocarbonyl isocyanates

2012 ◽  
Vol 90 (4) ◽  
pp. 333-343 ◽  
Author(s):  
Seiedeh Negar Mousavi ◽  
Davood Nori-Shargh ◽  
Hooriye Yahyaei ◽  
Kobra Mazrae Frahani
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Energy Difference ◽  
Basis Set ◽  
Hybrid Density Functional Theory ◽  
Total Dipole Moment ◽  
Functional Theory ◽  
Complete Basis Set ◽  
Conformation Stability ◽  
Hybrid Density Functional

Complete basis set CBS-QB3, hybrid-density functional theory (B3LYP/Def2-TZVPP) based methods and NBO interpretation were used to investigate the impacts of the stereoelectronic effects and electrostatic and steric interactions on the conformational properties of halocarbonyl isocyanates (halo = F (1), Cl (2), and Br (3)), halothiocarbonyl isocyanates (halo = F (4), Cl (5), and Br (6)), and haloselenocarbonyl isocyanates(halo = F (7), Cl (8), and Br (9)). Both methods showed that the Z-conformations of compounds 1, 4, and 7 are more stable than their corresponding E conformations, but the stability of the E conformations, when compared with the corresponding Z conformations, increases from compound 1 to compound 3, compound 4 to compound 6, and also from compound 7 to compound 9. The NBO analysis showed that the generalized anomeric effect (GAE) is in favor of the Z conformations of compounds 1, 4, and 7. The GAE values calculated (i.e., GAEE–GAEZ) increase from compound 1 to compound 3, compound 4 to compound 6, and also from compound 7 to compound 9. On the other hand, there are none of the same trends between the calculated total dipole moment and the Gibbs free energy difference values between the E and Z conformations (i.e., ΔμE–Z and ΔGE–Z) of compounds 1–3, 4–6, and 7–9. Accordingly, the GAE succeeds in accounting for the increase of the E conformation stability from compound 1 to compound 3, compound 4 to compound 6, and also from compound 7 to compound 9. Therefore, the GAE associated with the electron delocalization, not the total dipole moment changes (i.e., ΔμE–Z), is a reasonable indicator of the total energy difference in compounds 1–3, 4–6, and 7–9. There is a direct correlation between the calculated GAE and Δ[r2–6(E) – r2–6(Z)] parameters. Importantly, there are interesting through-space electron delocalizations (LP2X6→π*C4–O5) that justify the increase of the E conformation stability from compound 1 to compound 3, compound 4 to compound 6, and also from compound 7 to compound 9, when compared with their corresponding Z conformations. The correlations between the GAE, bond orders, total steric exchange energies (TSEE), ΔGZ–E, ΔμE–Z, structural parameters, and conformational behaviors of compounds 1–9 were investigated.

scholarly journals Study of Magnesium Diboride Clusters Using Hybrid Density Functional Theory

2008 ◽  
Vol 2008 ◽  
pp. 1-4 ◽  
Author(s):  
D. Rodríguez ◽  
D. Soto ◽  
E. Ramírez ◽  
A. Cruz ◽  
A. Santana ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Magnesium Diboride ◽  
Population Analysis ◽  
Equilibrium Structure ◽  
Basis Set ◽  
Hybrid Density Functional Theory ◽  
Functional Theory ◽  
Equilibrium Structures ◽  
Hybrid Density Functional

Using hybrid density functional theory and a relatively large basis set, the lowest energy equilibrium structure, vibrational spectrum, and natural orbital analysis were obtained for magnesium diboride clusters [(MgB2)x for x=1,2, and 3]. For comparison, boron clusters [Bx for x=2,4, and 6] were also considered. The MgB2 and (MgB2)2 showed equilibrium structures with the boron atoms in arrangements similar to what was obtained for pure boron atoms, whereas, for (MgB2)3 a different arrangement of boron was obtained. From the population analysis, large electron density in the boron atoms forming the clusters was observed.

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