All the semiempirical methods contain sets of parameters. Atomic and diatomic parameters exist in PM6, while MNDO, AM1, PM3, and MNDO-d use only single-atom parameters. Not all parameters are optimized for all methods; for example, in MNDO and AM1 the two electron one center integrals are normally taken from atomic spectra. In the following Table, parameters optimized for a given method are indicated by '*'. A '+' indicates that the value of the parameter was obtained from experiment (not optimized). Where neither symbol is given, the associated parameter is not used in that method.
Table of Parameters
Parameter | Description | Units |
MNDO |
AM1 |
PM3 |
PM6 |
Uss, Upp, Udd | s, p, and d atomic orbital one-electron one-center integrals |
eV |
* |
* |
* |
* |
βs, βp, and βd | s, p, and d atomic orbital
one-electron two-center resonance integral terms |
eV |
* |
* |
* |
* |
ξs, ξp, and ξd | s, p, and d Slater atomic orbital exponent | bohr-1 |
* |
* |
* |
* |
ξsn, ξpn, and ξdn | s, p, and d Slater atomic orbital internal exponent | bohr-1 |
* |
* |
* |
* |
αA | Atom A core-core repulsion term | Å-1 |
* |
* |
* |
|
αAB | Atoms A and B core-core repulsion term | Å-1 |
|
|
|
* |
Gss | s-s atomic orbital one
center two electron repulsion integral |
eV |
+ |
+ |
* |
* |
Gsp | s-p atomic orbital one
center two electron repulsion integral |
eV |
+ |
+ |
* |
* |
Gpp | p-p atomic orbital one
center two electron repulsion integral |
eV |
+ |
+ |
* |
* |
Gp2 | p-p' atomic orbital one
center two electron repulsion integral |
eV |
+ |
+ |
* |
* |
Hsp | s-p atomic orbital
one-center two-electron exchange integral |
eV |
+ |
+ |
* |
* |
KnA or anA | A Gaussian multiplier for nth Gaussian of atom A |
none |
|
* |
* |
* |
LnA or bnA | A Gaussian exponent multiplier Gaussian of atom A |
Å-2 |
|
* |
* |
* |
MnA or cnA | A Radius of center of nth Gaussian of atom A |
Å |
|
* |
* |
* |