# Difference between revisions of "AMBER forcefield"

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AMBER forcefield [1].

## Force field

$E_{\rm total} = \sum_{\rm bonds} K_r (r - r_{eq})^2 + \sum_{\rm angles} K_\theta (\theta - \theta_{eq})^2 + \sum_{\rm dihedrals} {V_n \over 2} [1 + {\rm cos}(n\phi - \gamma)] + \sum_{i

## Parameters

#### ff99

Param99 was developed for organic and biological molecules using the restrained electrostatic potential (RESP) approach to derive the partial charges: [3]

#### ff02

The ff02 force field is a polarisable variant of ff99. The charges were determined at the B3LYP/cc-pVTZ//HF/6-31g* level, and hence are more like "gas-phase" charges. [4]