AMBER Archive (2007)

Subject: Re: AMBER: Fwd: SCC convergence failure in QM-MM DFTB

From: M. L. Dodson (mldodson_at_houston.rr.com)
Date: Sun Aug 26 2007 - 10:42:14 CDT


Francesco Pietra wrote:
> Second addendum to the original (Subject) issue:
>
> Using a larger solventCap (25.0) and starting from pdb file for the solute
> which had been minimized by "ab initio" DFT with the most recent functionals
> with NWChem, sander bombed for the same reason somewhat earlier than with cap
> 20.0 and stating from pdb minimized by global conformational space MMFF94 and
> Amber9 simulated annealing. I add also the two last steps in the presumption
> they may help. DFTBESCF is about the same as for Cap 20.0, while all other
> energy values are higher (for 1951 WAT residues added for Cap 25.0, with
> respect to 947 residues for Cap 20.0). If useful, I add that DFT as said above
> never crashed.
>
>
> NSTEP = 2600 TIME(PS) = 5.200 TEMP(K) = 299.15 PRESS = 0.0
> Etot = -24120.4790 EKtot = 3566.8407 EPtot = -27687.3196
> BOND = 0.0000 ANGLE = 0.0000 DIHED = 0.0000
> 1-4 NB = 0.0000 1-4 EEL = 0.0000 VDWAALS = 2754.0573
> EELEC = -18926.0584 EHBOND = 0.0000 RESTRAINT = 9.0684
> DFTBESCF= -11524.3870
> EAMBER (non-restraint) = -27696.3881
> ------------------------------------------------------------------------------
>
>
> NSTEP = 2700 TIME(PS) = 5.400 TEMP(K) = 300.31 PRESS = 0.0
> Etot = -26475.7499 EKtot = 3580.5889 EPtot = -30056.3388
> BOND = 0.0000 ANGLE = 0.0000 DIHED = 0.0000
> 1-4 NB = 0.0000 1-4 EEL = 0.0000 VDWAALS = 2856.2068
> EELEC = -21370.9526 EHBOND = 0.0000 RESTRAINT = 8.8248
> DFTBESCF= -11550.4178
> EAMBER (non-restraint) = -30065.1636
> ------------------------------------------------------------------------------
>
> SANDER BOMB in subroutine eglcao <qm2_dftb_eglcao.f> :
> SCC Convergence failure - MAXITER exceeded.
> Exiting
>
>

To incorporate an answer to Professor Roitberg within a reply to
you, sander in amber9 cannot do box/PME simulations.

Now on to your simulation. I think we need some preliminary
answers, first. How did you get the structure you started with?

Professor Roitberg's suggestion to start with a structure that had
been minimized with AM1 seems to me a good one. Then you might
try a preliminary VACUUM SCC-DFTB minimization. If you cannot get
a SCF in vacuum, you are unlikely to get one with a water cap,
either.

The output given seems to indicate that the energy is dropping by
~2500 over a hundred steps, and coupled with the lack of major
changes in the QM energy, would seem to me to indicate the solvent
is doing some rearrangement. This would also seem to me to be
unrelated to the inability to achieve SCF, but I am open to
other suggestions by the QMMM experts that might read this posting.

This output is from an MD run. Did you not minimize the system
and do classical MD to relax the system to the force field? At
the very least you need some time with the classical FF to relax
the solvent voids created by LEaP. We need more information on
what you have done. In detail. Otherwise we are all just wasting
time.

Bud Dodson

>
>
>
> --- Francesco Pietra <chiendarret_at_yahoo.com> wrote:
>
>> Date: Sun, 26 Aug 2007 00:26:42 -0700 (PDT)
>> From: Francesco Pietra <chiendarret_at_yahoo.com>
>> Subject: Fwd: SCC convergence failure in QM-MM DFTB
>> To: Amber <amber_at_scripps.edu>
>>
>> Perhaps relevant to add to the issue below:
>>
>> ---solvateCap EQE TIP3PBOX {coordinates of a solute central atom} 20.0
>>
>> placed the solute right at the center of the spherical cap; though, along the
>> longer axis, the 98-atoms solute was not far from the spherical cap edge. I
>> wonder whether a much bigger cap should be set, and whether 20.0 present one
>> has hindered SCC convergence.
>>
>> --- I was surprised that DFTB MD used as as little memory as AM1 MD (ca 0.1%
>> of
>> the 4GB available per node). Having not yet read the DFTB theory in detail, I
>> am comparing to classical DFT, where modern functionals at modest 6-31G*
>> basis
>> set level, with the same 98-atoms molecule in vacuum, led to use all the
>> available memory (ad there was still much swapping). I understand that DFTB
>> working must be profoundly different from classical DFT.
>>
>> francesco
>>
>> --- Francesco Pietra <chiendarret_at_yahoo.com> wrote:
>>
>>> Date: Sat, 25 Aug 2007 10:54:12 -0700 (PDT)
>>> From: Francesco Pietra <chiendarret_at_yahoo.com>
>>> Subject: SCC convergence failure in QM-MM DFTB
>>> To: Amber <amber_at_scripps.edu>
>>>
>>> Now the 98-atoms solute is well inside TIP3PBOX cap (prepin from
>>> antechamber).
>>> After successful minimization with:
>>>
>>> Initial min for qmmm with dftb
>>> &cntrl
>>> imin=1, maxcyc=500, ncyc=200,
>>> cut=20.0, ntb=0, ntc=2, ntf=2,
>>> ivcap=0, fcap=10,
>>> ifqnt=1
>>> /
>>> &qmmm
>>> qmmask=':1',
>>> qmcharge=0,
>>> qmtheory=7,
>>> qmshake=0,
>>> qm_ewald=0
>>> /
>>>
>>> MD with:
>>>
>>> 300K constant temp for qmmd with dftb
>>> &cntrl
>>> imin=0, ntb=0
>>> cut=20.0, ntc=2, ntf=2,
>>> tempi=300.0, temp0=300.0,
>>> ntt=3, gamma_ln=1.0,
>>> nstlim=20000, dt=0.002,
>>> ivcap=0, fcap=10,
>>> ntpr=100, ntwx=100,ifqnt=1
>>> /
>>> &qmmm
>>> qmmask=':1',
>>> qmcharge=0,
>>> qmtheory=7,
>>> qmshake=0,
>>> qm_ewald=0
>>> /
>>>
>>> sander.MPI (mpirun -np 4) exited because:
>>>
>>> vlimit exceeded for step 2886; vmax = 26.4356
>>> SANDER BOMB in subroutine eglcao <qm2_dftb_eglcao.f> :
>>> SCC Convergence failure - MAXITER exceeded.
>>> Exiting
>>>
>>> Much obliged for suggestions what to do best. Thanks
>>>
>>> francesco pietra
>>>
>>>
>>>
>>>
>

-- 
M. L. Dodson
Email:	mldodson-at-houston-dot-rr-dot-com
Phone:	eight_three_two-five_63-386_one
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