Some methods are more sensible than others to specific features of the molecular structure. Then, you may experience the blowout with one and not with other. This may or may not be related to the appropriateness of the parameters.
In your case, since you mention that the molecule is very close to molecules existent in the parametrisation set, it seems more likely that the instabilities are being caused by the larger basis set. Maybe we need some more elaborated algorithm for this in the future?
One thing that *may* help is, before turning on AM1/d-PhoT, try running it for a while with a more robust model, such as AM1, until the system seems "equilibrated". This *may* get you past the point where the instabilities happen. Turning on AM1/d-PhoT after this point may be a smaller perturbation in the system.
Cheers,
Gustavo Seabra
On Thu Nov 15 2012 10:08:15 vojtech.mlynsky.upol.cz said:
> Dear all,
>
>
>
> .. thank you all for your suggestions and Mark for adding extra
> clarifications.
>
>
> Firstly, I have just completed another tests with qm_ewald=0 and larger
> qmcut values but it resulted with same problem. I have also tested what
> Gustavo suggested (slowly heating the system without qm_theory and then run
> subsequent equilibration with qm region // also starting from my classical
> MD restart file adding qmmm flag ..) but same issue occurred. That test
> starting from my MD restart 'survived' for ~10 ps QM/MM dynamics, but
> suddenly blows up after ..
>
>
>
>
> And indeed, it looks like SCF convergence problem. I obtain these SCF
> warnings in output files. As I have said, my system with the largest QM
> region could not be minimized because SCF convergence fails. I have already
> try to chance some parameters for that; namely turning pseudo_diag to 0,
> using larger itrmax (more SCF steps than 1000), changing ndiis_attempts to
> turn on earlier than on step 800 and also testing different diag_routines ..
> . but I none of these helped for particular system (QM region consists of
> 100 atoms). It still appears that SCF settings are adjusted wisely (as it is
> often stated in manuals).
>
>
>
>
> The pure Single-Point sqm test with of QM region structure with all default
> settings ends without any problem (pdb at the end of this mail if you want
> to have a look). I should point out that it is the geometry of QM region
> from starting structure. I will also try to check it for the geometry of QM
> region just before disruption during pre-heating phase. It is still
> interesting that it could be issue with SCF. It seems that I could
> interpreted it wrongly as QM region blows first and then SCF convergence
> (obviously) could not be achieved... I will also double-check that as well.
> Anyway, thank you again (Andreas) for pointing on that.
>
>
>
>
> With best regards,
>
> Vojtech
>
>
>
>
> ==============================
> Department of Physical Chemistry
> Palacky University Olomouc
> tr. 17. listopadu 12, 779 00 Olomouc
> Czech Republic
> ==============================
>
>
>
>
>
> QM region pdb:
>
>
>
>
>
> REMARK
>
> ATOM 1 C QMR 1 1.730 1.989 -1.062
>
> ATOM 2 H QMR 1 1.759 1.561 -2.104
>
> ATOM 3 O QMR 1 3.087 1.852 -0.530
>
> ATOM 4 C QMR 1 3.224 0.589 0.193
>
> ATOM 5 H QMR 1 4.050 0.026 -0.326
>
> ATOM 6 C QMR 1 0.874 1.090 -0.155
>
> ATOM 7 H QMR 1 0.566 1.616 0.797
>
> ATOM 8 C QMR 1 1.855 -0.103 0.109
>
> ATOM 9 H QMR 1 1.612 -0.720 1.021
>
> ATOM 10 O QMR 1 1.940 -0.981 -1.033
>
> ATOM 11 H QMR 1 1.229 -1.701 -0.996
>
> ATOM 12 O QMR 1 -0.349 0.680 -0.836
>
> ATOM 13 P QMR 1 -1.162 -0.562 -0.093
>
> ATOM 14 O QMR 1 -1.436 -0.142 1.344
>
> ATOM 15 O QMR 1 -0.476 -1.856 -0.449
>
> ATOM 16 O QMR 1 -2.633 -0.544 -0.861
>
> ATOM 17 C QMR 1 -3.442 -1.753 -0.586
>
> ATOM 18 H QMR 1 -3.510 -1.882 0.530
>
> ATOM 19 H QMR 1 -2.935 -2.635 -1.073
>
> ATOM 20 N QMR 1 1.574 0.033 7.582
>
> ATOM 21 C QMR 1 2.101 1.339 7.698
>
> ATOM 22 H QMR 1 2.680 1.657 8.596
>
> ATOM 23 N QMR 1 1.852 2.099 6.625
>
> ATOM 24 C QMR 1 1.141 1.272 5.746
>
> ATOM 25 C QMR 1 0.650 1.514 4.432
>
> ATOM 26 O QMR 1 0.833 2.643 3.807
>
> ATOM 27 N QMR 1 -0.038 0.481 3.815
>
> ATOM 28 H QMR 1 -0.445 0.633 2.876
>
> ATOM 29 C QMR 1 -0.234 -0.769 4.477
>
> ATOM 30 N QMR 1 -0.995 -1.699 3.821
>
> ATOM 31 H QMR 1 -1.324 -1.511 2.870
>
> ATOM 32 H QMR 1 -1.073 -2.643 4.194
>
> ATOM 33 N QMR 1 0.259 -1.056 5.735
>
> ATOM 34 C QMR 1 0.948 -0.037 6.336
>
> ATOM 35 N QMR 1 -1.327 -0.874 -7.845
>
> ATOM 36 C QMR 1 -0.154 -1.651 -7.713
>
> ATOM 37 H QMR 1 0.430 -1.994 -8.596
>
> ATOM 38 N QMR 1 0.147 -1.939 -6.433
>
> ATOM 39 C QMR 1 -0.870 -1.354 -5.676
>
> ATOM 40 C QMR 1 -1.118 -1.365 -4.247
>
> ATOM 41 N QMR 1 -0.307 -1.963 -3.378
>
> ATOM 42 H QMR 1 -0.530 -2.086 -2.377
>
> ATOM 43 H QMR 1 0.581 -2.382 -3.693
>
> ATOM 44 N QMR 1 -2.298 -0.723 -3.853
>
> ATOM 45 H QMR 1 -2.627 -0.778 -2.875
>
> ATOM 46 C QMR 1 -3.117 -0.098 -4.779
>
> ATOM 47 H QMR 1 -4.050 0.387 -4.361
>
> ATOM 48 N QMR 1 -2.931 -0.020 -6.087
>
> ATOM 49 C QMR 1 -1.805 -0.676 -6.553
>
> ATOM 50 H QMR 1 1.481 3.049 -1.122
>
> ATOM 51 H QMR 1 3.490 0.787 1.231
>
> ATOM 52 H QMR 1 -4.436 -1.605 -1.009
>
> ATOM 53 H QMR 1 1.616 -0.764 8.325
>
> ATOM 54 H QMR 1 -1.800 -0.552 -8.773
>
> END
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Received on Thu Nov 15 2012 - 07:00:03 PST
