About bond-length constrained geometry optimization

From NWChem

Viewed 76 times, With a total of 0 Posts
Jump to: navigation, search

Clicked A Few Times
Threads 3
Posts 5
Hello.
I'm trying to do DFT geometry optimization with fluorine-rich molecule, in negatively charged(-1) state.
But every time I run geometry optimization, somehow one of the fluorine falls out from the structure.
(I've tried several initial geometry, roughly optimized with MD, but didn't helped much)

After optimization, distance between the fallen out fluorine and the nearest carbon is approximately 2 aungstrom
This seems very unrealistic to me considering usual C-F bond is around 1.3~1.4 aungstrom

At this moment, I think I should run geometry optimization with a constraint, fixing bond-length of that troublesome C-F.
I checked the documentation and wrote script as below, but constraint didn't work and the troublesome fluorine fall out again.
I'd really appreciate if i can get some advices on fixing constraining bond-length script below.
(Note. I tried to fix carbon (Atom no. 4) and make spring-bond with F (Atom no. 15))

Of course, will also extremely appreciate other advices on how to deal with this "falling out" problem...
Thank you in advance!!

Sincerely.
SKIM.



echo

start molecule

title "Title"
charge -1

geometry units angstroms print xyz autosym
--
end

BASIS
 * library 6-31+g*
END

DFT
 xc b3lyp
ODFT
MULT 2
DIRECT
NOIO
CONVERGENCE rabuck
MAXITER 1000
END

MEMORY 100000 mb

DRIVER
MAXITER 1000
END

CONSTRAINTS fixf
fix atom 4
spring bond 4 15 50 13.8
END

task dft optimize
Edited On 9:27:23 PM PST - Tue, Nov 28th 2017 by Kswkoren


Forum >> NWChem's corner >> QMMM



Who's here now Members 0 Guests 0 Bots/Crawler 1


AWC's: 2.5.10 MediaWiki - Stand Alone Forum Extension
Forum theme style by: AWC