From owner-chemistry@ccl.net Thu Aug 27 04:12:01 2015 From: "Adedapo Adeyinka u11335132!A!tuks.co.za" To: CCL Subject: CCL: Empirical Dispersion Correction Message-Id: <-51624-150827040850-15081-NFaZS08/glcTn1Y+TXyF/Q-,-server.ccl.net> X-Original-From: Adedapo Adeyinka Content-Type: multipart/alternative; boundary=089e013d1d5ec3a8f4051e467979 Date: Thu, 27 Aug 2015 10:08:42 +0200 MIME-Version: 1.0 Sent to CCL by: Adedapo Adeyinka [u11335132++tuks.co.za] --089e013d1d5ec3a8f4051e467979 Content-Type: text/plain; charset=UTF-8 Dear all, I am trying to predict the protonation constants of some amine compounds using DFT methods. In order to describe solvation properly, I have used a number of explicit water molecules to represent the first solvation shell around the solute, then embedded this in the PCM continuum solvation model). Also I have used B3LYP, B3LYP-D3 and B97D functionals (and the 6-311++Gdp basis set) to carry out my structure optimizations since the importance of including dispersion corrections has been emphasized a lot in literature recently. Contrary to my expectations, I got the best predicted protonation constants with the B3LYP functional followed by B97D. The results that deviated most from experiment was that obtained with the B3LYP-D3. I have tried to find out why this was the case and so far the only lead I have got is that the empirical dispersion correction was designed to yield accurate isolated molecule energies and geometries. Does anyone know why my results followed this trend? Does this mean that since I have used explicit water molecules there is no need for dispersion correction to be included with the B3LYP functional? Thanks in advance for your contributions. -- Adedapo Adeyinka -- This message and attachments are subject to a disclaimer. Please refer to http://www.it.up.ac.za/documentation/governance/disclaimer/ for full details. --089e013d1d5ec3a8f4051e467979 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Dear all,
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 = =C2=A0 I am trying to predict the protonation constants of some amine compo= unds using DFT methods. In order to describe solvation properly, I have use= d a number of explicit water molecules to represent the first solvation she= ll around the solute, then embedded this in the PCM continuum solvation mod= el). Also I have used B3LYP, B3LYP-D3 and B97D functionals (and the 6-311++= Gdp basis set) to carry out my structure optimizations since the importance= of including dispersion corrections has been emphasized a lot in literatur= e recently. Contrary to my expectations, I got the best predicted protonati= on constants with the B3LYP functional followed by B97D. The results that d= eviated most from experiment was that obtained with the B3LYP-D3.=C2=A0
I have tried to find out why this was the case and so far the only l= ead I have got is that the empirical dispersion correction was designed to = yield accurate isolated molecule energies and geometries. Does anyone know = why my results followed this trend? Does this mean that since I have used e= xplicit water molecules there is no need for dispersion correction to be in= cluded with the B3LYP functional?

Thanks in advanc= e for your contributions.

--
Adedapo Adeyinka


This message and attachments are subject to= a disclaimer. Please refer to=20 http://www.it.u= p.ac.za/documentation/governance/disclaimer/ for full details. --089e013d1d5ec3a8f4051e467979--