See reference **[Schlegel91a] for a discussion** of SCF convergence and stability. The default is NoFinalIteration. For example assuming the geometry is close to the actual transition state would: Do a single point energy with IR selected. The non-linear Schrödinger equation and the non-locality of electrons make it difficult to understand what is actually occurring.

The CONVERGE **keyword behaves differently for different** computational tasks. Pass For in-core calculations, saves the integrals on disk as well, to avoid recomputing them in Link 1002. Another approach is useful when building large molecules: Start with a small core of your molecule and optimize it at the theory you desire. It may also be that your starting configuration was very close to a transition state, and the minimizer found that transition state (with a zero gradient/force) rather than the minima you

This is the default for HF and DFT. 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]). You can change the initial guess with the GUESS=CORE keyword. I think it will **work. Best wishes ** Kapil Dhaka Nov 16, 2014 Can you help by adding an answer?

NoFermi suppresses Fermi broadening and is the default. This is the default for direct SCF. Normally the scf took less than 80 cycles to converge. The error is Density matrix is not changing but DIIS error= 1.35D-02 CofLast= 3.25D-02.

In this case you may achieve better results with the GUESS=SAD keyword. (SAD stands for "superposition of atomic densities", a quick method for generating an initial wave function.) Sometimes molecules with DM Calls for use of the direct minimization SCF program [Seeger76]. This job will (most likely) run out of optimization cycles. First do a single point energy calculation with the IR property checked.

In this case you might see a few very small frequencies that (numerically) are very close to zero. Using the quadratic SCF (as stated below: scf=qc or scf=xqc) and taking of symmetry by using the NoSymm keyword solved the issue for me. If you have one or more geometry cycles displayed in the output dialogue, the problem is likely related to geometry optimization. (Of course, there may be exceptions, so examine the error INTEGRAL STORAGE OPTIONS Direct Requests a direct SCF calculation, in which the two-electron integrals are recomputed as needed.

If so, you may want to choose an unrestricted calculation by typing either the SCF=UNRESTRICTED or UHF keyword in the options filed in the calculation dialogue.. This uses slower but more stable algorithms with broader tolerances; this may help some difficult systems to converge. Join for free An error occurred while rendering template. For example, if a hydrogen is too close to a nitrogen, a bond may form (that you don't want) Recall that the bonds drawn on the screen mean absolutely nothing to

If you suspect this is the case, you should be able to double check this by resubmitting the molecule with another geometry optimization and with the gradient tolerance increased a bit. QPERR — A SYNTAX ERROR WAS DETECTED IN THE INPUT LINE. For some systems with metals the default guess is already a core guess. 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

XQC Add an extra SCF=QC step in case the first-order SCF has not converged. The best Hessian is one generated at the same theory level as the one you are attempting use for optimization. For example, recalculating force constants on the geometry obtained 1 or 2 steps before the error. After running > for 11 hours **the calculation** dies uncompleted and the output (copied > below) says that Density matrix is not changing but DIIS error and the > SCF is

Special Issues with Transition State Searches Spartan treats Transition State searches as a special case of geometry optimizations. A word ab coordinates While the simplest coordinate system for geometry optimization is Cartesian, Spartan will commonly use an internal coordinate system (sometimes referred to as “redundant internal coordinates” [RIC] or This also speeds up geometry optimizations by more than a factor of 2 for typical organic systems.

This is the default SCF procedure in Gaussian. One thing which has been successful in settling this problem is to add SCF=NoVarAcc so that all of the small integrals are included from the first iteration. 密度矩阵不收敛，但能量收敛了。说明轨道还不够合理，换个方法猜测轨道。但真正的原因还是小积分项忽略。 二、 可以试试：这是g03 d01以上版本才会出现的，c02及以下不会出现。 However attempting to use symmetry can sometimes cause difficulty in convegence. Sometimes clicking the 'Minimize button' a few times will force the symmetry to be more exact and also solve the problem. Keywords mentioned SCF=UNRESTRICTED, SCF=RESTRICTED HESS=UNIT GUESS=CORE GUESS=MIX SCFTOLERANCE=x PRINTLEV=2

Use this option to retain a specific state of the wavefunction throughout the calculation. You might have forgotten geom=check in the input file, or there may be a file name mismatch between the *.chk file in your directory and the %chk=*.chk in the input file. A geometry optimization ran out of cycles, how do I restart it? A less common explanation might be that the Hessian is not very accurate.

Try deselecting the Symmetry check box. Symmetry is causing a problem. Chances are good that if you spend some time with the hints mentioned above, you will overcome any computational obstacles that your specific system presents. 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 above approach is often useful when searching for transition states. But before you resubmit, examine the current conformation of the molecule. If you are not the intended recipient, and have received this > message in error, please notify us immediately by reply e-mail and > then delete it from your system. > For more information see below for more specifics.

For molecules where the multiplicity is unknown, people generally run an optimisation for each possible multiplicity and take the lowest energy arrangement to be the ground state. Run problems These errors The SCF is confused. MaxConventionalCycles=N Sets the limit on conventional SCF cycles during SCF=XQC to N. Here are the instructions how to enable JavaScript in your web browser.

This method is slower than regular SCF with DIIS extrapolation but is more reliable. For GVB and CASSCF calculations, SCF convergence is determined not by change in the density matrix, but rather in terms of the orbital change and energy change, respectively. Semi-empirical is fast and often very good, but it also may also suffer from poor approximations, and may not be good enough for your molecule.

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