CCL: smearing with NWChem

 Sent to CCL by: "Van Dam, Hubertus J" [HubertusJJ.vanDam^^^pnl.gov]
 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.txt