CCL: scan

From: "hadi behzadi" <hadi.behzadi++gmail.com>
Subject: CCL: scan
Date: Sat, 8 Sep 2007 12:13:37 -0400
 Sent to CCL by: "hadi  behzadi" [hadi.behzadi*_*gmail.com]
 Dear all,
 I am trying to do a PES scan for Fe-O distance between 1.75-8 A in heme with one
 and two water as a axial ligand. I have two problem in this relation as follow:
 1- For heme with one water the calculation give me error in 4.1 A because of
 failure to convergence, the energy profile is good befor this distance.I use
 SCF(maxcycle=5000) and the B3lyp method with the follow basis sets:
 n,o 6-31g*
 c,h sto-3g
 fe lanl2dz
 2- For heme with two water as a axial ligand,one water is fixed, the energy
 profile is not good due to the break in energy profile in 2.35 and 2.45 A. Here
 is the obtained energy and used basis sets:
 n,o,c,h 3-21g*
 fe lanl2dz
 Distance   Energy(A.U)
 1.75       -2392.47636390
 1.85       -2392.48624467
 1.95       -2392.48987980
 2.05       -2392.49028130
 2.15       -2392.48885147
 2.25       -2392.48631707
 2.35       -2392.48316683
 2.45       -2392.58475917
 2.55       -2392.58231643
 2.65       -2392.57967485
 2.75       -2392.57698884
 2.85       -2392.57434438
 2.95       -2392.57179832
 3.05       -2392.56938208
 3.15       -2392.56710231
 I really don t underestand what is the problem and any Help would be
 appreciated.
 Regards