Re: [AMBER] QM-MM Equilibration of the System

From: Gustavo Seabra <>
Date: Mon, 15 Jun 2015 13:26:31 -0300

Hi Brittany,

Have you thermalized you system previously, using regular MD? Yu should turn QM on only after the system is stable at the target temperature using regular MD.

Gustavo Seabra

On seg jun 15 2015 13:11:25 Brittany Boykin said:
> Hello users,
> I am conducting QM-MM using AMBER for my methyltransferase systems. I am having some trouble on the equilibration of the system for pressure and temperature using script eq_pt.csh. I used NSTEP: 50,000, dt= 0.001 with time step of 1fs first after running calculation for volume, script eq_v.csh. I then increased the steps to 500,000 to see is the calculation would converge. In both cases the system did not fully converge, as I keep receiving this Warning, shown below, several times. Also, the calculation completely ran in both cases.
> QMMM: Unable to achieve self consistency to the tolerances specified
> QMMM: No convergence in SCF after 1000 steps.
> QMMM: Job will continue with unconverged SCF. Warning energies
> QMMM: and forces for this step will not be accurate.
> QMMM: E = -0.8514E+06 DeltaE = 0.1002E+02 DeltaP = 0.1050E+00
> QMMM: Smallest DeltaE = 0.2486E+01 DeltaP = 0.6844E-01 Step = 47
> How can I fix this problem for each system so that I can continue to umbrella sampling?
> Thank you in advance?
> Brittany Boykin
> Graduate Student
> Auburn University
> Department of Chemistry and Biochemistry
> e:
> c: (404)545.1036
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Received on Mon Jun 15 2015 - 09:30:03 PDT
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