SPRING_V0

SPRING_V0 = [real (array)]

Default: SPRING_V0 = 0 for all coordinates with status=8 in ICONST.

Description: Rate at which the bias potential is shifted in [math]\displaystyle{ uc/fs }[/math].

Consider the bias potential for a molecular-dynamics (MD) run of the form:

[math]\displaystyle{ \tilde{V}(\xi_1,\dots,\xi_{M_8}) = \sum_{\mu=1}^{M_8}\frac{1}{2}\kappa_{\mu} (\xi_{\mu}(q)-\xi_{0\mu})^2, \; }[/math]

where the sum runs over all ([math]\displaystyle{ M_8 }[/math]) coordinates the potential acts upon ([math]\displaystyle{ \xi_{\mu}(q) }[/math]). The coordinates are defined in the ICONST file by setting the status=8. Optionally, the position of minimum ([math]\displaystyle{ \xi_{0\mu} }[/math]) can be shifted at a constant rate [math]\displaystyle{ \dot{\xi}_{\mu} }[/math] every MD step, i.e.,

[math]\displaystyle{ \xi_{0\mu}(t+\Delta t) = \xi_{0\mu}(t) + \dot{\xi}_{\mu}(q)\Delta t, \; }[/math]

where [math]\displaystyle{ \Delta t }[/math] is the time step used in MD (POTIM). The rate [math]\displaystyle{ \dot{\xi}_{\mu} }[/math] can be defined via the parameter SPRING_V0 and its units are [math]\displaystyle{ uc/fs }[/math], where [math]\displaystyle{ uc }[/math] corresponds to the units of the coordinate the potential acts upon (e.g., [math]\displaystyle{ {\AA} }[/math] for coordinates with flag R, [math]\displaystyle{ rad. }[/math] for coordinates with flag A, dimensionless for coordinates with flag W, etc...). The number of items defined via SPRING_V0 must be equal to [math]\displaystyle{ M_8 }[/math], otherwise the calculation terminates with an error message.

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