SemiEmpirical Parameters

INDO/1 -

• Atoms:
  H
  Li - F
  Na - Cl
  K - Zn
  Y - Cd
• Basis: valence s, p, & d orbitals; 2-center integrals 0; 1-center exchange integrals; Hµµ= -(IPµ - EAµ/2 + . . .; Hµv from STO-3G SCF
• Pros: transition metals, bond lengths, bond angles, singlet-triplet splitting, better electron spin
• Weakness: small rings favored, dye absorbances low, dissociation energies poor
• Typical Accuracy: .delta.Hf° ± 100 kcal/mol; length ± 0.08 Å

INDO/S -

• Atoms:
  Li, B - F
  P, S
  Sc - Zn
• Basis: parameterized for spectra

MINDO/3 -

• Atoms:
  H
  B - F
  Si - Cl
• Basis: 32 molecules; 1-center integral parameters; 3 & 4-center integrals on same; resonance integral from exp.
• Pros: carbocations, amides flat
• Weakness: valence s & p only; small rings favored; resonance energy low; no H-bonds; lone pair repulsion low; rings flat; transition states poor
• Typical Accuracy: .delta.Hf° ± 5 kcal/mol; dipole ± 0.5 Debye

MNDO -

• Atoms:
  H
  Li - F
  Al - Cl
  Cr, Zn, Ge, Br
  Sn, I
  Hg, Pb
• Basis: 32 molecules
• Pros: multiple bonds; EA¹s for ions; better lone pair repulsion; better angles
• Weakness: valence s & p only; no H-bonds; S, Cl, & Br IP high; activation barriers high; conjugation low; 3-center B bonds low; -O-O- bond short; C-O-C angle large; Ar-NO2 out of plane; amides pyramidal; no Van der Waals attraction; steric crowding disfavored
• Typical Accuracy: .delta.Hf° ± 11 kcal/mol, .delta.Hr ± 17 kcal/mol, .delta.HÝ ± 16 kcal/mol; dipole ± 0.3 Debye, IP ± 0.8 eV; length ± 0.07 Å, angle ± 5°, dihedral ± 17°

MNDO/d -

• Atoms:
  Na - Cl
  Ti, Fe, Ni, Cu, Zn, Ge - Br
  Zr, Pd, Ag, Cd, Sn - I
  Hf, Hg
• Basis: adding d-orbitals to MNDO; split valence; 11 parameters for sp elements; 15 parameter for spd elements; d orbitals for 2nd row main group
• Pros: Heat of formation; hypervalent shape
• Weakness: IP; dipole moment
• Typical Accuracy: .delta.Hf° ± 5 kcal/mol; dipole ± 0.4 Debye, IP ± 0.6 eV; length ± 0.06 Å, angle ± 2°

AM1 (Austin Model 1) -

• Atoms:
  H
  Li, B - F
  Al - Cl
  Zn, Ge, Br
  I
  Hg
• Basis: 100 molecules; 1-center from spectroscopy; minimal basis set; Gaussian patches; 7-21 parameters per element
• Pros: H-bonds; better activation barriers; hypervalent P; Heat of Formation 40% better; 2-Cl-THP axial (anomeric)
• Weakness: valence s & p only; no hypervalent compounds; P orbitals irregular @ 3Å; conjugate interactions low; -CH2- favored by 2 kcal; Heat of Hydrogenation low; dissociation enthalpies high; activation enthalpies high; -NO2 energies high; -O-O- bond short; H2O H-bond geometry wrong; H+ transfer barrier high; acrolein, glyoxal poor
• Typical Accuracy: .delta.Hf° ± 8 kcal/mol, .delta.Hr ± 5 kcal/mol, .delta.HÝ ± 6 kcal/mol; dipole ± 0.5 Debye, IP ± 0.6 eV; length ± 0.06 Å, angle ± 4°

SAM1 -

• Atoms:
  H
  C - F
  Si - Cl
  Fe, Cu, Br
  I
• Basis: AM1 w/ d-orbitals
• Pros: theoretical consistency; transition metals
• Typical Accuracy: .delta.Hf° ± 8 kcal/mol, .delta.Hr ± 5 kcal/mol; IP ± 0.4 eV; length ± 0.04 Å, angle ± 3°

SM2 (Solvation Model 2) -

• Atoms:
  H
  C - F
  P - Cl
  Br
• Basis: AM1, Aqueous in Hamiltonian

PM3 -

• Atoms:
  H
  Li, Be, C - F
  Mg - Cl
  Zn - Br
  Cd - I
  Hg - Bi
• Basis: 657 molecules; minimal basis set; 2 Gaussians for each element; 18 parameters per element
• Pros: hypervalent included; HOF 40% better; -NO2 better; geometries better; H2O H-bond geometry OK
• Weakness: partial charges unreliable; amides pyramidal, barrier low; IP's poor; H+ transfer barrier high; VdW attraction high; H-H core repulsion @ 2Å low
• Typical Accuracy: .delta.Hf° ± 8 kcal/mol, .delta.Hr ± 6 kcal/mol, .delta.HÝ ± 9 kcal/mol; dipole ± 0.6 Debye, IP ± 0.7 eV; length ± 0.05 Å, angle ± 4°

PM3(tm) -

• Atoms:
  H
  Li - F
  Mg - Cl
  Ca, Ti, Cr - Br
  Zr, Mo, Ru - Pd, Cd - I
  Hf - W, Hg
  Gd
• Basis: PM3 with d-orbitals; minimal basis set

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10/99 Ernie Chamot / Chamot Labs / / echamot@chamotlabs.com