From owner-nwchem-users@emsl.pnl.gov Fri Jul 21 11:26:50 2006 Received: from odyssey.emsl.pnl.gov (localhost [127.0.0.1]) by odyssey.emsl.pnl.gov (8.13.6/8.13.6) with ESMTP id k6LIQorY018121 for ; Fri, 21 Jul 2006 11:26:50 -0700 (PDT) Received: (from majordom@localhost) by odyssey.emsl.pnl.gov (8.13.6/8.13.6/Submit) id k6LIQoul018120 for nwchem-users-outgoing-0915; Fri, 21 Jul 2006 11:26:50 -0700 (PDT) X-Ironport-SG: OK_Domains X-Ironport-SBRS: 5.1 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AQAAALm4wESKPQEBAQEHBAoHBh0 X-IronPort-AV: i="4.07,169,1151910000"; d="scan'208"; a="2145196:sNHT22300684" Reply-To: From: "Chad Risko" To: Subject: FW: [NWCHEM] Electric field for finite field analysis Date: Fri, 21 Jul 2006 13:26:24 -0500 Message-ID: <002101c6acf3$2e9169f0$fd376981@VALUEDC38DAD41> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit X-Mailer: Microsoft Office Outlook 11 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2869 Thread-Index: AcalJA6oknn89+JhR/6Mtjasdru6FQHzZeAA Sender: owner-nwchem-users@emsl.pnl.gov Precedence: bulk All, Please find below the responses to my original question (see below). I would like to take the opportunity, as well, to thank Indranil Rudra, Robert Hinde, Antonio Ferreira, and Nicholas Labello for their helpful suggestions and prompt responses. Unfortunately, it looks as though I will not be able to perform the calculations that I had originally intended, as the use of point charges will not allow for proper analysis of the effect of an electric field for the systems (odd shapes) with which I am investigating; however, (as was suggested) there are some other options available to due such calculations. Cheers! Chad --- Original Post For a series of molecular systems with which I am investigating, I would like to apply a static electric field along the x-, y-, and/or z-directions - at the DFT level of theory and a fixed geometry - in order to observe the response of the system to the electric field (in particular, changes in the charge distribution and/or dipole moment); the purpose is to be able to use the finite field approach to look at the linear and nonlinear polarizabilities of the molecules. I have, as of yet, not been able to find keywords within the manual that allow for the application of a static electric field. Could you please inform me if this is possible with NWChem, and, if so, which keywords to utilize (also, in what units (a.u., etc.) the field parameters are entered)? --- You can use point charge to simulate electric field. Check the following input for Neon (taken from section B.2 Nwchem manual). An external field may be simulated with point charges. The charges here apply a field of magnitude 0.01 atomic units to the atom at the origin. Since the basis functions have not been reordered by the additional centers we can also restart from the previous vectors, which is the default for a restart job. restart ne title "Neon in electric field" geometry units atomic bq1 0 0 100 charge 50 ne 0 0 0 bq2 0 0 -100 charge -50 end task scf Best wishes, Rudra --- The following brief entry in the NWChem manual will help you. The URL is long so I will break it after a slash: http://www.emsl.pnl.gov/docs/nwchem/doc/user/ node42.html#SECTION004220000000000000000 Note that, in contrast to Gaussian and GAMESS, NWChem apparently does not have the capability to immerse a molecule in a pure dipole field (with all field gradients equal to zero). So "sandwiching" the molecule between two distant point charges seems to be the best alternative. You can vary the magnitude and distance of the point charges in such a way to keep the field at the origin constant but change the field gradients at the origin, and thereby test whether the (very small) nonzero field gradients affect the molecular response. Good luck! RJH --- We have used this approach for atomic systems in the development of basis sets for the calculation of (hyper)polarizabilities. I've copied Nick Labello on this as he's the graduate student who did most of the work and should have some good information for you. There is one caveat when doing calculations on molecular systems. Finite field calculations are valid only when the applied field is uniform across the entire molecule. Thus, individual point charges won't work. What you'll likely have to do is construct parallel sheets of point charges to construct the uniform field you'll need. This will be highly molecule-dependent and there's some careful planning needed to make sure you've gotten everything set up properly. I'll let Nick fill you in on the details. Tony --- As Dr. Ferreira said, there is no keyword available to turn on a uniform electric field in NWChem. In past work, we have used NWChem for finite field calculations on atoms only. A uniform electric field was crudely approximated with the use of two dummy atoms that contained equal and opposite charges (no basis functions or electrons) at such a distance from the atom so that the nuclei experienced a field of the correct strength (Usually 0.001 au). NWChem was extremely useful for this initial work as I was able to code the finite field equations and a basis function optimization scheme directly into the input deck using the python extensions. For single point molecular calculations (using the now optimized basis set) we used GAMESS, which has, I believe, exactly what you are looking for. There is a keyword available to either turn on a single electric field, or you may select the default finite field calculation which applies a number of fields and eventually returns a table with all of the static dipole and (hyper)polarizability elements in one run. ---