Parameters used in Semiempirical Methods

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

*

*

*

*
bs,  bp, and bd s, p,  and d atomic orbital one-electron
two-center resonance integral terms		 eV

*

*

*

*
xs, xp, and xd s, p, and d Slater atomic orbital exponent bohr-1

*

*

*

*
xsn, xpn, and xdn s, p, and d Slater atomic orbital internal exponent bohr-1

*

*

*

*
aA Atom A core-core repulsion term Å-1

*

*

*

 
aAB 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

 

*

*

*