PM3, or Parametric Method 3, is a semi-empirical method for the

quantum In physics, a quantum (: quanta) is the minimum amount of any physical entity (physical property) involved in an interaction. The fundamental notion that a property can be "quantized" is referred to as "the hypothesis of quantization". This me ...

calculation of molecular electronic structure in

computational chemistry Computational chemistry is a branch of chemistry that uses computer simulations to assist in solving chemical problems. It uses methods of theoretical chemistry incorporated into computer programs to calculate the structures and properties of mol ...

. It is based on the Neglect of Differential Diatomic Overlap integral approximation. The PM3 method uses the same formalism and equations as the AM1 method. The only differences are: 1) PM3 uses two Gaussian functions for the core repulsion function, instead of the variable number used by AM1 (which uses between one and four Gaussians per element); 2) the numerical values of the parameters are different. The other differences lie in the philosophy and methodology used during the parameterization: whereas AM1 takes some of the parameter values from spectroscopical measurements, PM3 treats them as optimizable values. The method was developed by J. J. P. Stewart and first published in 1989. It is implemented in the MOPAC program (of which the older versions are public domain), along with the related RM1, AM1, MNDO and MINDO methods, and in several other programs such as Gaussian,

CP2K CP2K is a freely available ( GPL) quantum chemistry and solid state physics program package, written in Fortran 2008, to perform atomistic simulations of solid state, liquid, molecular, periodic, material, crystal, and biological systems. It prov ...

, GAMESS (US), GAMESS (UK), PC GAMESS, Chem3D, AMPAC, ArgusLab, BOSS, and SPARTAN. The original PM3 publication included parameters for the following elements: H, C, N, O, F, Al, Si, P, S, Cl, Br, and I. The PM3 implementation in the SPARTAN program includes PM3tm with additional extensions for transition metals supporting calculations on Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Mo, Tc, Ru, Rh, Pd, Hf, Ta, W, Re, Os, Ir, Pt, and Gd. Many other elements, mostly metals, have been parameterized in subsequent work. A model for the PM3 calculation of lanthanide complexes, calle
Sparkle/PM3
was also introduced.

References

* * * * *For a recent review, *{{cite journal, journal=Chemical Physics Letters, year=2006, volume=425, issue=1–3, pages= 138–141, doi=10.1016/j.cplett.2006.04.103, title=Modeling rare earth complexes: Sparkle/PM3 parameters for thulium(III), last1=Freire, first1=Ricardo O., last2=Rocha, first2=Gerd B., last3=Simas, first3=Alfredo M., bibcode = 2006CPL...425..138F Semiempirical quantum chemistry methods