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If you have an open shell system you may need to add the MIX keyword to construct a better guess. In general we suggest using the Minimizer (the Minimize button in the Spartan interface uses molecular mechanics to reduce straing energy and 'clean up' molecules that have been constructed by hand), The non-linear Schrödinger equation and the non-locality of electrons make it difficult to understand what is actually occurring. It does steepest descent and then scaled steepest descent as in SCF=QC, but then switches to regular SCF instead of quadratic convergence, using the quadratic algorithm only if the regular SCF

NoIncFock prevents the use **of incremental Fock** matrix formation, and it is the default for conventional SCF. Running out of cycles usually implies that you had a bad starting guess, or that some unexpected chemistry is occurring (such as bond breaking). It is possible that the initial wavefunction is bad. Often Spartan's default Hessian (a semi-empirical guess) is good enough.

This is usually due to precision problems so the CONVERGE keyword may help. SCF=QC is not available for restricted open shell (RO) calculations. The default value for N is 2. Multiplicity Are there unpaired electrons?

A number of examples of using **this can** be found in Chapter 11 of our Spartan '16 Tutorial and User's Guide. (Also see the sections on Spartan Reaction Database and Transition A less common explanation might be that the Hessian is not very accurate. QPERR — A SYNTAX ERROR WAS DETECTED IN THE INPUT LINE. This will result in there being slightly fewer molecular orbitals than there are basis functions.

Gaussian is very particular about the structure of the *.com input file. This turns on a number of more flags which often lead to better stability, at the cost of slower performance. The very first thing to try is to select the the "Converge" check box in the calculations dialogue. You can use molecular mechanics in the Spartan interface (the Minimize button), or any other theory from the Calculations dialogue. (Make sure to select the "Frozen Atoms" box next to the

So i used scf=(Maxconventionalcycles=100,xqc) which resulted in a good compromise between using scf=qc and optimisation speed. You can choose a conservative Hessian with the HESS=UNIT keyword. O, H, C, S, .... georgia_mcgaughey*|*merck.com" wrote: > > Sent to CCL by: "McGaughey, Georgia B." [georgia_mcgaughey{}merck.com] > Sarah, > > Have you tried any other key words?

CDIIS implies Damp as well. Big Turns off optional O(N3) steps to speed up very large calculations (>5000 basis functions). You are *almost* at the minima but the gradient is not sufficiently small. This is not advised for geometry optimizations.

i.e. It is also possible that the algorithm is seeking the minima (or transition state) at a higher level of precision than you need. A geometry optimization ran out of cycles, how do I restart it? InCore Insists that the SCF be performed storing the full integral list in memory.

It shows that **Gaussian has 6 MW free** memory but the computational requres 106 MW. Ali African Institute for Mathematical Sciences Senegal Katia Meirelles Universidade Federal de Mato Grosso (UFMT) Views 720 Followers 6 Answers 4 © 2008-2016 researchgate.net. Multiple keywords are separated by spaces. Once a good starting point is found a good Hessian is required.

However, for efficient transition state searches the importance of a good starting geometry and a good Hessian are especially critical. It will **take a while if** they are huge. I'm giving an overview below. 1/ - SCF=qc will probably solve the problem, albeit at a cost - Change the SCF converger to either SD, Quadratic or Fermi 2/ - lower

- The SCF is confused.
- Pass For in-core calculations, saves the integrals on disk as well, to avoid recomputing them in Link 1002.
- In the case of the DIIS error the scf always took more than 100 cycles before the error, so by adding scf=(Maxconventionalcycles=100,xqc) the scf switched to qc after 100 cycles in
- What to do when this occurs?
- See reference [Schlegel91a] for a discussion of SCF convergence and stability.
- Start simple It is always good advice to start by using a lower theory level.

The strategy of starting small and working up to larger molecules and methods applies to transition state searching. If the SCF looks like it has stopped converging, but the "Error" is not decreasing, you may need to change the tolerance. The DIIS algorithm may not work properly if the HOMO/LUMO gap falls under 0.5 eV and does not work at all when the SMEAR option is invoked. At times the job may be converging normally, just slowly, and one only needs to resubmit a job that has 'run out of cycles'.

Read our cookies policy to learn more.OkorDiscover by subject areaRecruit researchersJoin for freeLog in EmailPasswordForgot password?Keep me logged inor log in with ResearchGate is the professional network for scientists and researchers. This takes into account the standard bonding of tetrahedral sp3 and planar-like sp2 systems. This is not advised for geometry optimizations. As mentioned above this is not advised for geometry optimizations, and if used should only be done for the first few geometry cycles.

Depending on your available memory, Spartan will autmatically switch to an alternate algorithm (developed by Q-Chem, Inc.) for systems with more than 151 basis functions [assumes 512 MB available RAM]). Examining this output can yield several clues, you should see both the energy and the "DIIS error" slowly decrease. Try CIS=direct in your input file to prevent this or specify the amount of disk space to use in your input file. Kinetic Control tutorial (from Chapter 11 of the Spartan '16 Tutorial and User's Guide provide good examples of this strategy.

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