Sent to CCL by: "Chunhui Li" [baotogo2004/a\gmail.com] Hi, Dear All, I run a geometry opt job twice starting from the same structure. One result gave me a structure like V shape, but the other gave me a structure like O shape by forming a hydrogen bond. The setup for these two jobs are exactly same. I wonder how I can find out which one is the "right" one. I don't have experimental results to compare with. Here are some job details: The hydrogen bond is between water and F atom on a flurocarbon. Flurocarbon and water are coordinated with Fe3+. I am using Spartan HF 6-31G*.(I am going to use DFT, but I thought I may have the same problem.) I didn't include solvent effect. I want to know what would be the good practice to do in this situation. and also, I don't have good literature access, could anybody tell me the "exact" bond length for the hydrogen bond between F and H-O-H? Thank you very much in advance! -LilyE-mail to subscribers: CHEMISTRY=-=ccl.net or use: http://www.ccl.net/cgi-bin/ccl/send_ccl_message E-mail to administrators: CHEMISTRY-REQUEST=-=ccl.net or use http://www.ccl.net/cgi-bin/ccl/send_ccl_messagehttp://www.ccl.net/chemistry/sub_unsub.shtml Before posting, check wait time at: http://www.ccl.net Job: http://www.ccl.net/jobs Conferences: http://server.ccl.net/chemistry/announcements/conferences/ Search Messages: http://www.ccl.net/htdig (login: ccl, Password: search)http://www.ccl.net/spammers.txt RTFI: http://www.ccl.net/chemistry/aboutccl/instructions/

On Mon, Apr 28, 2008 at 12:22 PM, Lukasz Cwiklik cwiklik~!~gmail.com <owner-chemistry(!)ccl.net> wrote:

Sent to CCL by: "Lukasz Cwiklik" [cwiklik[-]gmail.com]
On Mon, Apr 28, 2008 at 4:27 PM, Chunhui Li baotogo2004 ~~ gmail.com
<owner-chemistry|a|ccl.net> wrote:
>
> Sent to CCL by: "Chunhui Li" [baotogo2004/a\gmail.com]
> Hi, Dear All,
>
> I run a geometry opt job twice starting from the same structure. One result gave me a structure like V shape, but the other gave me a structure like O shape by forming a hydrogen bond. The setup for these two jobs are exactly same. I wonder how I can find out which one is the "right" one. I don't have experimental results to compare with.

Dear Lily,
Most likely none of your structures is "right", however, the one with
lower energy is better than the other. This is the only criterion. In
practice, your problems indicate that the HF method combined with your
basis set is to simple the properly describe your system.
If you minimize a system you should check the minimum with
another/better method/basis (for example, check your HF minimum with
any method which accounts for electron correllation - even DFT with
local functional and small basis can be a good test).

Best,
Lukasz

--
Lukasz Cwiklik
http://cwiklik.wordpress.com

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