a sharp rise in energy

General discussion of the Cambridge quantum Monte Carlo code CASINO; how to install and setup; how to use it; what it does; applications.
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s.nasiri
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Joined: Sun Jun 02, 2013 11:41 am

a sharp rise in energy

Post by s.nasiri »

Dear All
I study the potential energy curve for ionic molecules such as LiH+ . For this molecule I see a sharp rise in energy at R=8 (au). Could anyone help me?

Thanks
Mike Towler
Posts: 239
Joined: Thu May 30, 2013 11:03 pm
Location: Florence
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Re: a sharp rise in energy

Post by Mike Towler »

Hi S.,

I don't think I'm being unreasonable if I make a sort of general request (not just to you, but to many people who post on here) - but if you ask for help then (a) you need to give us all the information we require in order to solve your problem in your first email - don't make us drag it out of you through multiple email requests - especially when it's obvious that we're going to need it and that we're not telepathic, and (b) please give at least some evidence that you've actually thought about the problem. I don't mean this as a criticism but, you know, if I was sending a question to 600-N people, that's what I would do.

You say: 'For the [LiH+] molecule I see a sharp rise in energy at R=8 (au). Could anyone help me?'

What does this even mean? If you measure it? If you do a VMC calculation? DMC? DFT? Lennard-Jones potential? What?

Show us a graph. Tell us what instrument/method/basis set/computational conditions you're using. What code? Which version of it? You could even attach some input and output files.. (one before and one after the sharp rise in energy).

If you do this you're much more likely to get an answer..

Mike

PS: Sorry I've been unable to find time to respond to some other posts recently - I don't think I've ever been as busy as this week. Is there no-one out of the 600-N who can substitute when I'm out of commission? This isn't (or shouldn't) be the 'Ask Mike and Neil' forum.. ;)

PPS: I know Katharina answered one the other week. Thanks! Saved me a job..
s.nasiri
Posts: 16
Joined: Sun Jun 02, 2013 11:41 am

Re: a sharp rise in energy

Post by s.nasiri »

Dear Mike

Thanks for your reply and I apologize for the unclear email. In fact I study potential energy curve for LiH+ molecule and the trial wave function constructed by the b3lyp/ccpvtz. some of the results are bring in the following. The computed energy (DMC) for R=9 or 10 is similar to the energy of R=8. Error for DMC computation is about 1E-5.

Your Sincerely
Saeed Nasiri


R................DFT(ha).............VMC............DMC
6.00000......-7.787667..........-7.4739......-7.779728
7.00000......-7.787598..........-7.4768......-7.779383
8.00000......-7.787712..........-7.2897......-7.478980
Last edited by s.nasiri on Fri Mar 27, 2015 1:47 pm, edited 2 times in total.
Mike Towler
Posts: 239
Joined: Thu May 30, 2013 11:03 pm
Location: Florence
Contact:

Re: a sharp rise in energy

Post by Mike Towler »

The door to the sitting room at 221b Baker Street flew open. A singular-looking man of rugged countenance skidded on the doormat, Mrs. Hudson clucking at his heels.

"Are you Mister Holmes?" he ejaculated. "The famous consulting detective?"

"I am he." said my friend, remaining remarkably calm.

"There's been a murder, sir! A foul, dastardly murder."

"I see. Do you have any further information you can impart?"

"No I don't."

"Then.." said Holmes, leaping up, rapidly equipping himself with overcoat, hat and cane. "Lead me to the crime scene, my good man. We have work to do."

"I hardly think that's necessary, Mister Holmes. Everyone is aware of your reputation. Surely you can simply name the fiend who did this without leaving your premises?"

With a sigh my friend reached for the bottle of liquid cocaine he habitually kept on the mantelpiece and slumped into his favourite armchair. It was clear he knew it would be a long night.
s.nasiri
Posts: 16
Joined: Sun Jun 02, 2013 11:41 am

Re: a sharp rise in energy

Post by s.nasiri »

Dear Mike
Thanks for your attention. However I can't understand your reply ???
Mike Towler
Posts: 239
Joined: Thu May 30, 2013 11:03 pm
Location: Florence
Contact:

Re: a sharp rise in energy

Post by Mike Towler »

[injects cocaine; breathes deeply]

What I'm trying to say -- through the use of a somewhat tortured analogy -- is that you have still not supplied us with anywhere near enough information.

You say:

Post 1 : "I get a sharp rise in energy.."

Post 2 : "..when I do VMC or DMC calculations.." [includes some numbers to show that - indeed - you get a sharp rise in energy]

Now clearly you know that it's almost certainly not supposed to do that, so either you've discovered some hideous bug in CASINO which no-one has ever encountered before (!) or you're doing something wrong. Before I can investigate either of these possibilities, I need to know exactly how you're doing these calculations. Thus you need to post the input and output files and the version of the CASINO (I presume it's CASINO?!?) and whatever other stuff I asked for in my earlier mail.

[slumps unconscious under the armchair]

M.
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