sanya
sanya@photonics.ru
Your molecule is in fact a fragment of a crystal structure. Are you sure the multiplicity of your cluster is 2? Are you sure that clusters of this type really exist in the gas phase? In crystals, such structures are surrounded by other atoms and, therefore, have no free valences, in contrast to your cluster.
Again and again: If you're trying to simulate a fragment of a crystal within some cluster approach, take care of capping your cluster properly. Otherwise, even in you force SCF to converge, the result will be far from reality.
An alternative way is to use plane-wave packages for periodic calculations. But, please, don't ask me about these packages, I have no experience of using them!
On Sun Jan 10 '10 11:22am, luxiaohua wrote
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>I optimize some molecule structure, but it don't converge even though I add some keyword. such as diis=.t. damp=.t. shift=.t. and so on. it still don't change.