B3LYP keyword

Molecular frequencies depend on the second derivative of the energy with respect to the nuclear positions. Analytic second derivatives are available for the Hartree-Fock (HF keyword). Density Functional Theory (primarily the B3LYP keyword in this book), second-order Moller-Plesset (MP2 keyword) and CASSCF (CASSCF keyword) theoretical procedures. Numeric second derivatives—which are much more time consuming—are available for other methods. 

Optimize the structure of acetyl radical using the 6-31G(d) basis set at the HF, MP2, B3LYP and QCISD levels of theory. We chose to perform an Opt Freq calculation at the Flartree-Fock level in order to produce initial force constants for the later optimizations (retrieved from the checkpoint file via OptsReadFC). Compare the predicted spin polarizations (listed as part of the population analysis output) for the carbon and oxygen atoms for the various methods to one another and to the experimental values of 0.7 for the C2 carbon atom and 0.2 for the oxygen atom. Note that for the MP2 and QCISD calculations you will need to include the keyword Density=Current in the job s route section, which specifies that the population analysis be performed using the electron density computed by the current theoretical method (the default is to use the Hartree-Fock density). 

The keyword for a given density-functional method is formed by concatenating the symbols for its exchange and correlation functionals. For example, combining the Becke three-term (B3) exchange functional with the Lee-Yang-Parr (LYP) correlation functional leads to the popular B3LYP density functional method. 

Keywords silacyclobutanes, pyrolysis, silenes, rearrangement, 3,4-benzo-1-silacyclobutenes, 2-silaindanes, B3LYP/6-31G calculations... 

This indicates that in SCN the order of nucleophilicity isS > N C (which is what any chemist would expect). Sulfur is the softest atom here, and carbon the hardest. The results of such a calculation vary somewhat with the method/basis (e.g. HF/6-31G, MP2/6-31G, etc.), and especially with the way the charges/electron populations are calculated. Here are the functions from the use of electrostatic potential charges (the G98 keyword Pop=MK was used) again using B3LYP/6-31 + G ... 

Keywords DFT Hybrid functionals Crystalline solids Transition metal oxides B3LYP... 

Obtained at the MP2/6-31G(d) level of theory using appropriate symmetry constraints and B3LYP/6-31G(d) thermodynamic corrections. Transition state structures were located using the TS or QST3 keyword. 

Keywords DFT B3LYP Transition state Openshell Diketopiper-azine Dioxirane Hydroxylation PES Radical Diradical... 

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