From owner-chemistry@ccl.net Tue Apr 13 15:19:01 2010
From: "Ol Ga eurisco1^-^pochta.ru" <owner-chemistry(_)server.ccl.net>
To: CCL
Subject: CCL:G: OPT fails in a big tungsten-phosphors compound and others
Message-Id: <-41652-100413151450-21493-Qmi97+gpaeFN5cFJ6DNycA(_)server.ccl.net>
X-Original-From: "Ol  Ga" <eurisco1 _ pochta.ru>
Date: Tue, 13 Apr 2010 15:14:49 -0400


Sent to CCL by: "Ol  Ga" [eurisco1..pochta.ru]
Dear YUNPENG LU,

Concerning questions 1 and 2 - you have very bad initial structure. To treat 
the situation you should increase the distance between atoms mentioned in 
your out file after "Small interatomic distances encountered:".

Also you can make a FREQ(NORAMAN) calculation to look how modify the 
structure to search local minima. OPT(RCFC) is also very suitable after 
freq(noraman).

OPT=verytight is too strict. The default convergence criteria is pretty 
good. Anyway if your search of local minima is successfull, you can switch 
to opt=tight. Criteria cab not solve your problem with "bad" distances. 

Sincerely,

Ol Ga


>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Sent to CCL by: "YUNPENG LU" [yunpeng2000-x-gmail.com]
Dear CCL Users,

Recently, I have helped an research group in my department to calculate an 
organometallic compound's geometry and its absorption spectra in solvent. 
The compound contains three tungsten atoms (W), and carbon, hydrogen, 
oxygen, phosphorus, and sulfur.But I have a lot of problems:

1) PBE1PBE converge problem

The geometry optimization was firstly done with BP86 and B3LYP in Gaussian 
03, the basis set I use for tungsten is LANL2DZ, and 6-31G(d) for the rest 
atoms. Both optimization were done successfully. Because the crystal 
structure of the compound has been determined, I can compare the geometrical 
values from the calculations to assess the quality of model chemistry. To my 
disappointment, both calculations are not good. The calculated P-P bond is 
2.348 from BP86, and 2.318 from B3LYP as the P-P distance in crystal is 
2.138. The P-W bond are 2.609, 2.754 from BP86,and 2.640, 2.762 from B3LYP 
as the P-W bond in crystal are 2.512, 2.611. (Bond distance are all in 
Angstrong.)

My first questions is at what reasonable difference between crystal data and 
theoretical value one can say that the geometry optimization is of good 
quality? I read several papers recently about the validations of DFT 
functionals but all are using gas phase measurements for comparisons.I read 
the paper by Dr. P. Jeffrey Hay, in Journal of Physical Chemistry A 2002, 
106, 1634, "Theoretical Studies of the Ground and Excited Electronic States 
in Cyclometalated Phenylpyridine Ir(III) Complexes Using Density Functional 
Theory", as he has provided some comparison about the geometry optimization 
and the crystal data for different Ir(III) compounds.While his calculation 
results shows that the difference of bond distance is usually very small.I 
just wander how that can happen as one is gas phase calculation but the 
other is condensed phase structure.So what is a reasonable criteria for 
comparison?

I realize that B3LYP and BP86 may not be good and I tested the same basis 
with PBE1PBE in Gaussian 03. The final result from PBE1PBE calculation make 
me difficult to conclude it is converged or not. From the energy values for 
the intermediate runs at the last several steps, they don't change but 
converge to a value. But the log file from Gaussian 03 finally shows:
===================================================================
 Maximum Force 0.001708 0.000002 NO
 RMS Force 0.000193 0.000001 NO
 Maximum Displacement NaN 0.000006 YES
 RMS Displacement NaN 0.000004 Y