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Free-energy calculations - Theoretical Biophysics Group

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33 BEUTLER ET AL. (1994)<br />

34 ZACHARIAS ET AL. (1994)<br />

<strong>Free</strong>-<strong>energy</strong> perturbation <strong>calculations</strong> “Alchemical transformations”<br />

Solution: Modification of the parametrization of the van<br />

der Waals term in the potential <strong>energy</strong> function that governs<br />

the interaction of an appearing, or disappearing,<br />

atom, i, with an unaltered one, j: 33<br />

U vdW<br />

ij<br />

(rij; λ) = 4 ɛij λ n ×<br />

⎧<br />

⎪⎨<br />

1<br />

<br />

⎪⎩ αvdW (1 − λ) 2 62 rij<br />

+<br />

σij<br />

−<br />

1<br />

αvdW (1 − λ) 2 ⎪⎬<br />

6 rij<br />

+ ⎪⎭<br />

σij<br />

Or equivalently, 34<br />

U vdW ⎡⎛<br />

(rij; λ) = 4ɛij(1 − λ) ⎣⎝<br />

σ2 ij<br />

r2 ⎞6<br />

⎛<br />

⎠ − ⎝<br />

ij + αλ<br />

σ2 ij<br />

r2 ⎞3<br />

⎠<br />

ij + αλ<br />

⎤<br />

⎦<br />

Possibility to scale interactions with different schedules.<br />

Chris Chipot <strong>Free</strong>-<strong>energy</strong> <strong>calculations</strong><br />

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