Re: Error : components of colvar "alpha" does not support system force calculation

From: Jérôme Hénin (
Date: Fri Apr 07 2017 - 07:06:36 CDT

Hi Souvik,

The combination of extendedLagrangian and ABF- that is, eABF - is not
considered experimental anymore. You'll find more tests and explanations
about it in these articles:

For that, I would recommend the latest version of the colvars module, that
is, at least that of NAMD 2.12.

You can also use this coordinate in other biasing methods, such as US and


On 7 April 2017 at 10:47, Souvik Sinha <> wrote:

> Hi,
> I am trying to set up an ABF calculation with "alpha" as RC. But there I
> get this error which tells me system force calculation is not available in
> colvar componenet "alpha". But to run ABF, force on the colvar needs to be
> calculated beforehand.
> In a previous thread in NAMD Mailing-list
> *
> <>*
> I found that turning on *extendedLagrangian * formalism is a possible
> way. But there was one disclaimer that "this is still considered a bit
> experimental".
> So, I am confused that whether I should use it or not unless I get to
> know the risk. So, can anyone enlighten me in this regard?
> One more thing I need to add, is it ok if I use "alpha" as RC in Umbrella
> sampling or Metadynamics using colvar module?
> Thanks.
> --
> Souvik Sinha
> Research Fellow
> Bioinformatics Centre (SGD LAB)
> Bose Institute
> Contact: 033 25693275

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