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° | QuantumMechanics | - | Set quantum mechanics method |
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| Command | | Argument | | Datatype | | Default | | Min |
| Max | |
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| Format: | | QuantumMechanics | Method = MNDO | AM1 | PM3 | | STRING | | - | | - | | - | | |
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| Python: | | QuantumMechanics(method) | | ||||||||||
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| Menu: | | Options > Quantum mechanics | | ||||||||||
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| Related: | | FormEnergy , Optimize |
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| Required: | |
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The QuantumMechanics command sets the semi-empircal method used to calculate
formation energies and
optimize geometries.
Calculations are performed by YAPAC, a specialized module derived from MOPAC,
originally developed by James P. Stewart, with several extensions and bug fixes added during development.
The methods AM1 and PM3 are extensions to the original MNDO approach and generally more accurate.
- The AM1 method should be used to optimize molecular geometries. Contrary to PM3, the difficult planar sp2 conformation of nitrogens is predicted well (e.g. the arginine side-chain is flat).
- The PM3 method has been optimized to reproduce experimental formation energies and consequently performs best there. It should not be used to optimize molecular geometries, as the ability of nitrogens to adopt the planar sp2 conformation is underestimated, e.g. the arginine side-chain is not recognized as planar.
Example 1:
QuantumMechanics MNDO
Use the MNDO (Modified Neglect of Diatomic Overlap) method for quantum mechanics calculations.
Example 2:
QuantumMechanics AM1
Use the AM1 (Austin Model 1) method.
Example 3:
QuantumMechanics PM3
Use the PM3 (Parametric Model 3) method.