I do not know the geometry of your molecule, but is it possible to simply confine it to CS symmetry? That would be the simplest way to keep your molecule flat.
On Mon Mar 3 '14 8:33am, pejer wrote
>I try to optimize my oligomer molecules without make it twisted (keep it flat) which means being optimize in two dimensions. I try:
>1) using cartesian, by input the value of z coordinate cartesian into 0.00000000 for every atoms, then freeze this z of every atoms.
>Although manual said that Cartesian couldn't be freezed, I found it on the contrary in another place in this web (classic.chem.msu.su/gran/gamess./marek/en/.../PCG-Tutorial-Usage.pdf) and this works for benzene (consists of 18 atoms), but fails for larger molecules (consists of 50 atoms).
>2) using z-matrix, by input value of dihedral angles for every atoms into 0 or 180 degrees, then freeze this dihedral of every atoms.
>- input every dihedral angles (using format in manual) in IFREEZ, fails when input for 49 dihedral angles, but succeed when input for 1 dihedral angle
>- input every dihedral angles in IFZMAT, but it showed error messages "BAD ZMAT INPUT". Also, the DLC couldn't be performed.
>I want to ask and ask for any suggestion,
>1) Is there any problem in my input? Is there any limitation number of freezing atom/variable? Is there another menu that I could add?
>2) Is there another strategy to optimize large molecules and keep it flat (optimize in 2D)? I work with molecules consists of n*50 atoms, the same molecules of other persons on a publication which using GAUSSIAN 03 package. They succeed to optimize oligomer in 2D.