Sent to CCL by: "Kalju Kahn"
[kalju:+:chem.ucsb.edu]
Joshi,
Are you sure that you need B3LYP/3-21G* geometry for this
structure?
Seems like molecular mechanics with MM3 might be better suited for
optimizing a large hydrocarbon.
If you need DFT geometry for some reason, try to freeze all
dihedrals and
optimize bond distances and angles
first. Small deviations of
torsional
angles around single bonds is more acceptable than an
unusually stretched
bond for calculation of some molecular
properties.
Kalju
Dear CCLers;
Hi
I am optimizing a
molecule having 387 atoms (only C and H atoms) which
includes neatly 16 methyl groups as substitutions in G03w, and the
method
is b3lyp/3-21g*. During the optimization the Maximum
Force
and RMS Forces are sometimes
converging, Maximum
Displacement and RMS   Â
Displacements are not converging and the
molecules energy is
oscillating. I am using following keywords in route
section as
%mem=1500mb
%nproc=4
#p
opt=(gdiis,maxcycle=200) b3lyp/3-21g* scf=maxcycle=500
Please give me suggestion
Thanks in advance
Joshi
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Dr. Kalju
Kahn
Department of Chemistry and Biochemistry
UC Santa Barbara, CA 93106
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