From owner-chemistry@ccl.net Wed Dec 23 06:44:01 2009 From: "=?ISO-8859-1?Q?Ulf_Ekstr=F6m?= uekstrom^-^gmail.com" To: CCL Subject: CCL: Isolated molecules & unoccupied orbitals: does the basis set matter? Message-Id: <-40957-091223064110-12532-NqlbW7MN85srHBY35BpeTg##server.ccl.net> X-Original-From: =?ISO-8859-1?Q?Ulf_Ekstr=F6m?= Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=ISO-8859-1 Date: Wed, 23 Dec 2009 12:40:59 +0100 MIME-Version: 1.0 Sent to CCL by: =?ISO-8859-1?Q?Ulf_Ekstr=F6m?= [uekstrom|-|gmail.com] > Is it possible that plane-wave and local-basis set codes behave > somehow differently concerning unoccupied orbitals? If so, why? Yes, because these (~Rydberg) orbitals can be very very large, and are typically not included in standard basis sets. In this sense the plane wave basis is better, until you hit the boundary of your unit cell. You don't mention which basis set you use, but if you try to increase it by adding more diffuse functions (some programs can do this auto- matically) you will most likely find your plane wave states also in your localized orbital calculations. It can happen that your state that is too high with the small basis will come down in energy with a more appropriate basis. Sincerely, Ulf Ekstr=F6m, VU University Amsterdam.