Molecular Mechanics Force Fields
- Atoms:
H, D
B - F
Si - Cl
Ca, Cr, Co, Cu - Br
Sr, Rh, Pd, Cd, Sn, Te, I
Pb
- Basis: XRD & ND Structures; 75 parameters; 3rd Order Dihedral term; bond dipoles vs electrostatic
- Pros: covalent, organic, Ground States
- Weaknesses: metal bonding, excited states, transition states
- Typical Accuracy: .delta.Hf° ± 0.5 kcal/mol, .delta.Hr ± 0.4 kcal/mol, .delta.HÝ ± 2 kcal/mol; dipole ± 0.1 Debye; length ± 0.03 Å, angle ± 1°, dihedral ± 8°
in Oxford Molecular's CAChe software.
- Atoms:
H
Li - F
Na - Cl
K, Ti - Br
Rb, Zr - I
Cs, W - Bi
Nd, Sm
U
- Modified MM2
in CambridgeSoft's Chem3D software.
- Atoms:
H
Li - F
Na - Cl
K - Br
Rb - I
Cs - La, Hf - At
- Basis: includes ¼ calculation; multicoordinate centers
- Atoms:
H
Li, C - O
Na, Mg, P, S
K, Ca
Rb, Sr, I
Cs, Ba
- Basis: 4th order dihedral
- Pros: accuracy, cyclohexylamine conformation, entropy by vibrational analysis, F-C-C-F hyperconjugation
- Typical Accuracy: .delta.Hf° ± 0.6 kcal/mol, .delta.Hr ± 0.4 kcal/mol, .delta.HÝ ± 1 kcal/mol; dipole ± 0.07 Debye; length ± 0.01 Å, angle ± 1°, dihedral ± 8°
in Tripos' SYBYL program.
- Atoms:
H, He
Li - Ne
Na - Ar
K - Kr
Rb - Xe
- Basis: biomolecules, harmonic force field
- Pros: biomolecules, saturated HCs
- Weakness: inorganics, unsaturations, nonbond attractions high, 2-Cl-THP eq. (no anomeric)
- Typical Accuracy: .delta.Hr ± 1 kcal/mol, .delta.HÝ ± 1 kcal/mol
in the AMBER suite of programs from Kollman, UCSF.
- Atoms:
H
C - F
Na, Mg, P - Cl
K, Ca, Fe, Cu, Br
Rb, I
Cs
- Basis: biomolecules, harmonic force field, 25 parameters, united atom charges
- Pros: proteins/DNA, aqueous
- Weakness: inorganic
- Typical Accuracy: .delta.Hr ± 0.7 kcal/mol
in Martin Karplus' CHARMm program, Harvard University.
- Atoms:
H
C - O
Na - S
K - Fe
Rb
Eu
- Basis: 18 parameter force field
- Pros: biopolymers
- Typical Accuracy: .delta.Hr ± 0.9 kcal/mol
in Oxford Molecular's Nemesis program.
in Walker & Mills' FUNGUS program.
- Atoms:
H
Li, Be, O
Na - Si, Cl
K - Ni, Zn, Ge, Br
Rb - Nb, Cd, Sn, I
Cs- La, Nd, Eu-Tb, Ho, Yb-Hf
Pu
in MSI's Cerius II software.
- Atoms:
H
B - F
Na, Al - Cl
Ca, Fe, Zn - Br
In - I
- Basis: Bonds from atomic radii, angles from hydrides, harmonic force field
- Pros: General organic & main group
- Weakness: Accuracy, nonphysical charges, 2-MeO-THP equilibrium
- Typical Accuracy: .delta.HÝ ± 2 kcal/mol, .delta.Hr ± 1 kcal/mol; length ± 0.03 Å, angle ± 3°, dihedral ± 8°
in Biosym/MSI's Discover software.
- Atoms:
H
C-F
Na, Si-S, Ar
Ca, Br
I
- Basis: ab initio data, nondiagonal force field, crossterms, generalized parameters
- Weakness: 2-MeO-THP equatorial
- Typical Accuracy: .delta.Hf° ± 2 kcal/mol, .delta.Hr ± 0.5 kcal/mol, .delta.HÝ ± 0.8 kcal/mol; length ± 0.01 Å, angle ± 2°; solubility parameter ± 0.2, sorption energy ± 5 kcal/mol
in Biosym/MSI's Discover software.
- Atoms:
H - He
Li - Ne
Na - Ar
K - Kr
Rb - Xe
Cs - Rn
- Basis: diagonal valence; rule based (electronegativity, atomic radii, hardness, scaling, d-p ¼ bonding; organics, inorganic, organometallic & biomolecules
- Pros: any element; organometallic complexes
- Weakness: accuracy
Back to Periodic Table.
/ echamot@chamotlabs.com