Re: QMMM convergence/optimization issues in CHCL3 solvent

From: Mariano Spivak (
Date: Tue Nov 23 2021 - 10:47:07 CST

Hi Francesco,

>From this email, it is not quite clear what simulation you are trying to run.
Is this a QM/MM of your organic molecule (QM) in explicit CHCl3 (MM)?
If so, then you should not include implicit solvent in your QM calculation, because you already accounting for solute-solvent interactions through the NAMD interface.
Also adding optimization to the QM/MM config line is not recommended to say the least. It defeats the purpose of the method and will give you wrong results.

Hope this helps


> On Nov 23, 2021, at 10:26 AM, Francesco Pietra <> wrote:
> An organic molecule of 28 CHON atoms could be optimized, with all positive frequency analysis, with latest ORCA 5 at level
> PBE0 RIJCOSX D4 def2-TZVP Opt Freq tightscf defgrid2 CPCM (CHLOROFORM)
> With QMMM 100 cycles in CHCl3, starting from an MD quasi equilibrated .pdb in that solvent, at level
> PBE0 RIJCOSX D4 def2-TZVP defgrid2 enGrad CPCM
> one of the tree rings of the molecule, and only that, underwent rapidly extreme distortion, even against the sp3 sp3 sp protocols.
> Adding optimization (is that permitted with QMMM?), i.e., level
> ## ORCA
> # qmConfigLine "! MORead"
> qmConfigLine "! PBE0 RIJCOSX D4 def2-TZVP Opt tightscf defgrid2 CPCM"
> # qmConfigLine "%%moinp \"........gbw\""
> qmConfigLine "%%maxcore 5000"
> qmConfigLine "%%scf Maxiter 500 end"
> qmConfigLine "%%geom Maxiter 500 end"
> qmConfigLine "%%pal nproc 47 end"
> qmConfigLine "%%output Printlevel Mini Print\[ P_Mulliken \] 1 Print\[P_AtCharges_M\] 1 end"
> rapid scf convergence was observed. However, at the ORCA GEOMETRY RELAXATION STEP
> Warning: the length of the step is outside the trust region - taking restricted step instead
> The input lambda is .... -862.826127
> iter: 1 x= -888.315690 g= 0.656919 f(x)= 16.744573
> ......................
> ......................
> iter: 101 x=-1512.546611 g= 0.000257 f(x)= 0.000000
> [file orca_gstep/orca_gstep.cpp, line 790]: Error (ORCA_GSTEP): The lambda equations have not converged
> Does that suggest any adjustment? After a couple of hours of thinking, I am short of ideas
> Thanks for advice
> francesco pietran MD

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