Dear Benjamin As Emilio says, Mulliken analysis is very sensitive to the basis. In principle a DZP basis should give you a result going in the right direction. For a well converged DZP basis for water you obtain charges of the order of:
Species: O Atom Qatom 1 6.590 Species: H Atom Qatom 2 .723 3 .718 This is refered to the number of valence electrons (6 in O, 1 in H). I would suspect that your basis is either very poor (perhaps very short orbitals) or that you might have some other problem in the input (is the molecular geometry correct??). Regards, Marivi On 14 Jul 2005, at 3:32 PM, Benjamin Rogers wrote: Dear Emilio, Thanks for your reply. I understand that Mulliken analysis is very sensitive to the basis set. However, I would not have expected the use of any valid basis set to effectively result in the reversal of the polarity of the bond. Or perhaps I am interpreting the results incorrectly? With regards to the basis set etc., I am using the example input file and pseudopotentials supplied with Siesta. This file uses the default double zeta plus polarization basis set. Regards, Ben -----Original Message----- From: Siesta, Self-Consistent DFT LCAO program, http://www.uam.es/siesta [mailto:[EMAIL PROTECTED] On Behalf Of Emilio Artacho Sent: 14 July 2005 12:56 To: SIESTA-L@LISTSERV.UAM.ES Subject: Re: [SIESTA-L] Dear Benjamin Without enetering the details of your calculations, the Mulliken analysis gives numbers that can be very sensitive to the basis set used. Emilio Benjamin Rogers wrote: Dear All, I am attempting to perform Mulliken analysis on some molecular systems, however I am becoming confused by the output of Siesta. As an example, consider the Mulliken output from the calculation of water using the pseudopotentials and input file provided in the examples folder. This indicates a valence charge on the oxygen of 5.717 and a valence charge on each hydrogen of 1.142. This seems to disagree with conventional thought of the oxygen atom having a high electronegativity, which would result in it having a valence charge above 6 in water. In addition, Mulliken analysis from GAMESS given at http://www.chem.swin.edu.au/modules/mod5/annot_h2o_g.html indicates a charge on oxygen of 8.274 (a valence charge of 6.274) and a charge on hydrogen of 0.863. This appears to conform to the conventional description of water, and is therefore as expected. Can anyone please explain the Siesta results? Thank you in advance, Ben. This message has been checked for viruses but the contents of an attachment may still contain software viruses, which could damage your computer system: you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation. -- Emilio Artacho Department of Earth Sciences, University of Cambridge Downing Street, Cambridge CB2 3EQ, UK Tel. (+44/0) 1223 333480, Fax (+44/0) 1223 333450 [EMAIL PROTECTED], http://www.esc.cam.ac.uk/~emilio This message has been checked for viruses but the contents of an attachment may still contain software viruses, which could damage your computer system: you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation. Marivi Fernandez-Serra Departement de Physique des Materiaux Universite Claude Bernard Lyon 1, 43, bld du 11 novembre 1918 69622 Villeurbanne - France E-mail: [EMAIL PROTECTED] Phone: +33 4 72 431565 --------------------------------------------- Department of Earth Sciences University of Cambridge Downing Street Cambridge CB2 3EQ Phone: ( +44 ) 1223 333400 Fax: ( +44 ) 1223 333450
