Optimization at CBSQB3 level of theory, freezing specific dihedral angle?

03 March 2017 4 7K Report

I am trying to optimize my system (23 atoms) at CBSQB3 level of theory, freezing a specific dihedral angle in order to avoid the formation of hydrogen bond.

I run the calculation in a cluster (%nprocessor=4; %mem=32GB) and the structure of my input file is the following:

---------------------------------

# CBS-QB3 ccsd=maxcyc=256 Int=UltraFine freq opt(addredun)

Name of the job

Charge and Multiplicity

Cartesian Coordinates of the system

D X1 X2 X3 X4 F

-------------------------------

Obviously X1-X4 are the number of the atoms who describe the dihedral angle observed by Gaussview.

I got my final optimized geometry without any errors (Normal termination of the calculation) but the optimized geometry is identical respect to my starting geometry (only two optimization steps).

I used several times the command opt(addredun) for DFT calculation (B3LYP/6-311+G(d,p)) but this is the first time with CBSQB3 level of theory.

Someone knows if my command line could work with this level of theory?

Which command line do you use to freeze dihedral angles with CBSQB3 level of theory?

Thanks in advance for your availability and time

Debasish Mandal

CBS-QB3 is a composite method. If I remember correctly the first step for it is the B3LYP/CBSB7 optimization. So, If you are using B3LYP/6-311+G(d,p) optimized geometry as starting geometry probably there is nothing wrong if it is optimize in two step.

Manuel Petroselli

Thanks for your answer Debasish Mandal.

You remember well. The first optimization step using CBSQB3 level of theory is a DFT optimization and for this reason I thought my command line could work.

Unfortunately my optimized geometry was the same of my starting geometry. I think this is pretty weird and no possible (same angles, distances, dihedral angles for every atoms or atom groups).

I am pretty sure something is wrong but I do not know where and what.

David Shobe

I suppose you could always test it by submitting a related job in which you have moved one of the atoms (not involved in the dihedral angle being frozen) somewhat. If it still "optimizes" in 2 steps, then something is wrong. But likely, your initial B3LYP/6-311+G(d,,p) geometry was sufficiently optimized to begin with.

Manuel Petroselli

Thanks David Shobe.

I have already run that calculation but really thanks for the gread suggestion.

I will let you know the result ;)

Are radical HAT reactions (metal complexes have not to be involved) possible in H2O?

error in running a model in Abaqus

error in modelling model in Abaqus

MD MOE RMSD

MD MOE RMSD

MGL tools

fatal error

fatal error

fatal error

fatal error

flexibility of polymers chain