Re: [AMBER] MCPB, negative force constant?

From: Pengfei Li via AMBER <>
Date: Fri, 17 Nov 2023 14:07:34 -0600

Hi Matthew,

Based on my understanding, the negative force constant is usually due to that the bond recognition was not correct, there might be a mismatch of the fchk file and the PDB file in terms of the atom sequence.


> On Nov 17, 2023, at 2:51 AM, Matthew Guberman-Pfeffer <> wrote:
> Dear Amber community,
> MCPB reported a negative angle force constant in the second modeling step, even through all the frequencies in the Gaussian calculation were positive.
> MCPB set the negative force constant to zero. My questions are: Why did I get a negative force constant? Are the parameters not trustworthy? What could I do to fix this issue?
> Best,
> Matthew

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Received on Fri Nov 17 2023 - 12:30:02 PST
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