CCL:G: OPT fails in a big tungsten-phosphors compound and others

 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