From owner-chemistry@ccl.net Sun Nov 27 19:13:00 2011
From: "Saurabh S Chitnis sschitnis%x%gmail.com" <owner-chemistry-$-server.ccl.net>
To: CCL
Subject: CCL: questions on convergence, restarting jobs, counterpoise
Message-Id: <-45929-111127170210-2902-aTpKAAVAUeNvfKwPyi46Iw-$-server.ccl.net>
X-Original-From: "Saurabh S Chitnis" <sschitnis-,-gmail.com>
Date: Sun, 27 Nov 2011 17:02:07 -0500


Sent to CCL by: "Saurabh S Chitnis" [sschitnis _ gmail.com]
Hello, 

I have three questions:

1. In many of my "opt" and "freq=raman" jobs, I find that the calculation completes successfully with 
the forces having converged but the displacements still being above the convergence threshold. How 
can this be fixed? I usually face this problem when using opt=verytight and int=ultrafine.

2. Is there any way of restarting an analytic frequency job which has completed but not converged?

3. Can the output of a counterpoise calculation (i.e. the Corrected total energy) be interpreted as a 
bond-dissociation energy between the two fragments?

Here are some details regarding the above questions:

theory: DFT (B3LYP, PBE1PBE and B3PW91)

basis-set: cc-pvtz and aug-cc-pvtz

systems being calcualated: P2Me4, [P2Me5]+ and [P2Me6]2+

for the couterpoise: I'm trying to get the P-P bond dissocation energy. So I optimize the geometry as 
per usual and then redefine the optimized P2Me4 as fragment1(Me2P) and fragment2(PMe2) to run 
the counterpoise calculation. The result should be the homolytic bond dissociation energy right?

cheers
Saurabh