Computational Chemistry

attempted transition metal parameterization of PM3, PM3(tm), and the successors to PM3, namely PM5 and PM6. 6.2.5.4 MNDO MNDO [ ...

The two-electron integrals are evaluated applying ZDO (Section6.2.1) within the framework of the NDDO approximation (Section6.2. ...

The parameterb(Eq.6.17) for a valencesAO. The parameterbfor a valencepAO. The parameterain the correction increment (f(RAB), (E ...

Variations on the basic MNDO are MNDO/d and MNDOC, both developed by the research group of Thiel. MNDO/d has d functions added t ...

considerably exaggerate the barriers (assuming high-level ab initio calculations are correct here!). High-level calculations are ...

acceptable is a matter of judgment. Dewar et al. chose to call their modified MNDO method AM1, rather than MNDO/2, because they ...

suite carries it. AM1/d was modified and parameterized for P, S and Cl to give a variant called AM1* [ 69 ]. 6.2.5.6 PM3 and Ext ...

MNDO AM1 PM3 PM5 Heat of formation 77 50 42 25 kJ mol"^1 Bond length 0.066 0.053 0.065 0.051 A ̊ Bond angle 6.298 5.467 5.708 5. ...

Gaussians (an STO-3G basis set) as in standard ab initio calculations (Section5.3.2). This is in contrast to AM1, where the two- ...

and nucleic acids, which a few years ago were limited to molecular mechanics, can now be done routinely [ 89 ] with semiempirica ...

The accuracy of AM1 and PM3 then, is quite good for bond lengths and angles, but fairly approximate for dihedrals. The largest e ...

Table 6.1 Errors in AM1, PM3, and MP2(fc)/6–31G* bond lengths and angles, from Fig. 6.2 . Errors are given as AM1/PM3/MP2. In so ...

Table 6.1 (continued) a" aexp Bond length errors, r" rexp ,A ̊ Bond angle errors C–H O–H, N–H, S–H C–C C–O, N, F, Cl, S Angles 0 ...

error in dihedrals (Table6.2), omitting the PM3 result for HOOH, is 16(PM3 for FCH 2 CH 2 F). From Fig.6.2and Table6.1, the mea ...

are essentially improved versions of MNDO. The general impression is that the semiempirical and ab initio transition states are ...

geometries of the reactants and products (energy minima) are quite good, taking the MP2/6-31G results as our standard. The semie ...

(below). AM1 heats of formation for hypervalent compounds (above and reference [ 47 ]) appear to be distinctly inferior to those ...

heats of formation (298 K, gas phase) are (Z)¼"29.7 kJ mol"^1 ,(E)¼"47.7 kJ mol"^1 , i.e. (Z)"(E)¼18.0 kJ mol"^1 [ 94 ]. The com ...

magnitude of energy differences. Further information on the reliability of these methods is provided by the calculations for the ...

however, this is likely to be due to an atypical cancellation of errors. The transition state relative energies are best-approxi ...