Sent to CCL by: "Van Dam, Hubertus J" [HubertusJJ.vanDam{}pnl.gov]
Hi Frank,
I agree with you on the spin state. The S2 value does not seem to be affected
much by the smearing so that is probably OK. The units of the eFermi energy are
indeed Hartrees (i.e. atomic units).
With respect to rerunning any calculations did you also see Phil Hasnip's
comments on "cold smearing" total energy estimates (Phil thanks for
those). You might be able to use those to estimate the zero temperature total
energies (rather than rerunning your single point energies). If you have missed
Phil's message then please ping me directly and I will forward the message to
you. The one thing that does worry me is that the energy of the calculations
with smearing come out higher than the ones without. At present I don't
understand why that happens which makes me feel uneasy about this (which is why
I am not sure about rerunning calculations either). However, I have received a
test case from Adam Pelzer (thanks for providing that Adam) which I am running
at the moment and I hope to have a handle on this soon.
As far as the zero-point corrections are concerned I simply don't know how much
of a difference that will make. If the temperature is small you would think it
should not make a big difference but I don't know. So I would recommend just
trying it out on a single molecule and see what you find.
Best wishes,
Huub
-----Original Message-----
From: owner-chemistry+hubertus.vandam==pnl.gov_+_ccl.net [mailto:owner-chemistry+hubertus.vandam==pnl.gov_+_ccl.net] On Behalf Of Dr.
Xiaofeng (Frank) Duan duanx.ctr++afrl.hpc.mil
Sent: Thursday, April 07, 2011 7:42 AM
To: Van Dam, Hubertus J
Subject: CCL: FW: smearing with NWChem
Sent to CCL by: "Dr. Xiaofeng (Frank) Duan" [duanx.ctr+*+afrl.hpc.mil]
Hi Huub and Niri,
Thanks much for your comments and suggestions.
In my case, I did see the energy increase with smearing and did not see
much spin state change. Take one case as example:
1. With default smear value (0.001):
....
sigma= .10D-02 eFermi= -0.31098 T*S= 0.00E+00 nel(1)= 53.00 nel(2)=
52.00
....
Total DFT energy = -756.386904455476
....
<S2> = 0.7658 (Exact = 0.7500)
2. Without smear:
Total DFT energy = -756.388015008368
.....
<S2> = 0.7666 (Exact = 0.7500)
In above 1, is eFermi= -0.31098 the correction to the total energy in
unit au?
Anyway, I will take your suggestions to re-run single point calculations
with the largest smear value and multiplicity preservation for all the
structures.
One more question, I also did vibrational frequencies to get thermal
corrections. Do you think I need re-do frequencies with the same smear
value to get consistent results, or it is OK to keep these thermal
corrections?
Thanks,
Frank
On 04/06/11 19:32, Van Dam, Hubertus J HubertusJJ.vanDam.[].pnl.gov wrote:
Sent to CCL by: "Van Dam, Hubertus J" [HubertusJJ.vanDam[-]pnl.gov]
Hi Frank,
In addition to my earlier post I am forwarding some additional comments from
Niri Govind. Please have a look below.
Best wishes,
Huub
-----Original Message-----
From: Govind, Niri
Sent: Wednesday, April 06, 2011 4:25 PM
To: Van Dam, Hubertus J; CCL Subscribers
Cc: nwchem-users^emsl.pnl.gov
Subject: RE: smearing with NWChem
Hi Frank,
Try the following if you want to preserve the multiplicity with smear.
dft
mult 3
...
...
end
set dft:spinset t
task dft
Best regards,
-Niri
-----Original Message-----
From: owner-nwchem-users^emsl.pnl.gov [mailto:owner-nwchem-users^emsl.pnl.gov] On Behalf Of Van Dam, Hubertus J
Sent: Wednesday, April 06, 2011 4:08 PM
To: CCL Subscribers
Cc: nwchem-users^emsl.pnl.gov
Subject: [NWCHEM] RE: smearing with NWChem
Hi Frank,
This is an interesting question. There are a few specific points here:
1. The energy that is associated with the smearing is normally supposed to be
negative, so the total energies with smearing should be lower than the ones
without smearing.
2. The smearing functionality may change the spin state of your system. As you
are working on transition metal complexes I am guessing you might have open
shell systems. I can provide some special directives to control this if needed.
3. The code will actually print the energy that it adds on as a result of the
smearing. Search for "eFermi=" in the output. (see also 4.)
4. However, if you subtract the energy from 3. you will not get the energy you
are looking for. The problem is that the DFT energy for a system with
fractionally occupied orbitals is higher than the energy of the same system with
integer occupations. So the eFermi term that is added on corrects for that
difference and adds a bit more on top of that.
5. Concluding it seems to me that your best bet is to run all calculations with
the same smearing parameter for the final energies and compare the resulting
energies.
I am sorry if this is not the answer you were looking for. If you want any more
specific information please feel free to contact me.
Best wishes,
Huub
________________________________________
From: owner-chemistry+hubertus.vandam==pnl.gov^ccl.net
[owner-chemistry+hubertus.vandam==pnl.gov^ccl.net] On Behalf Of Xiaofeng Frank
Duan duanx:_:asc.hpc.mil [owner-chemistry^ccl.net]
Sent: Wednesday, April 06, 2011 1:12 PM
To: Van Dam, Hubertus J
Subject: CCL: smearing with NWChem
Sent to CCL by: "Xiaofeng Frank Duan" [duanx^asc.hpc.mil]
Hello,
I optimized some transitional metal compounds with DFT in NWChem. For some
compounds, I had to use "smear" to get SCF converged even though I
decreased "smear" values gradually to the minimum. Since 'smear' adds
an additional energy term, the total energy is higher than that of the
"zero smear" for the same structure.
My question is: How to correct or scale the "smeared" total energy to
the "zero smeared" one so that I can compare energies among different
compounds.
Thanks,
Frankhttp://www.ccl.net/cgi-bin/ccl/send_ccl_messagehttp-:-//www.ccl.net/chemistry/sub_unsub.shtmlhttp-:-//www.ccl.net/spammers.txthttp-:-//www.ccl.net/cgi-bin/ccl/send_ccl_messagehttp-:-//www.ccl.net/chemistry/sub_unsub.shtmlhttp-:-//www.ccl.net/spammers.txt>;