From owner-chemistry@ccl.net Tue Jun 2 19:32:00 2015 From: "Frank Oellien Frank.Oellien]~[gmail.com" To: CCL Subject: CCL: European Conference on Computational Chemistry - Extended Deadline Message-Id: <-51420-150602175141-20082-ywmcg8G7J1EX3JLdV1sswQ||server.ccl.net> X-Original-From: "Frank Oellien" Date: Tue, 2 Jun 2015 17:51:40 -0400 Sent to CCL by: "Frank Oellien" [Frank.Oellien===gmail.com] Dear Colleagues, We would like to remind you that the deadline for the abstract submission for oral presentations for the EuCO-CC 2015 has been extended to June 20th. We once more cordially invite you to join the 10th European Conference on Computational Chemistry, August 31 September 3, 2015 in Fulda, Germany that will reflect and highlight recent developments and trends in computational and theoretical chemistry and their impact on applied sciences. You can also submit research telegrams and posters until end of June. These are the conference topics: Drug Design meets Theoretical Chemistry Computational Chemistry of Biomolecules and Biological Systems Computational Material Sciences Electronic Structure and Complex Properties of Molecular Systems Molecular Dynamics and Kinetics Quantum Mechanics and Molecular Mechanics Condensed Phase Catalysis and Inorganic Systems Virtual Environments in Computational Sciences We are glad to confirm the complete list of invited speakers: Margareta Blomberg, Stockholm, Sweden Ria Broer, Groningen, The Netherlands Richard Friesner, New York, USA Holger Gohlke, Dusseldorf, Germany Alexander Hillisch, Bayer Healthcare, Germany Benedetta Menucci, Pisa, Italy John Mitchell, St. Andrews, UK Christian Ochsenfeld, Munich, Germany Maria Joao Ramos, Porto, Portugal Gabor Terstyanszky, London, UK Walter Thiel, Mulheim an der Ruhr, Germany The procedure as well as the template for submission is available on the conference homepage http://www.euco-cc-2015.org/ Kind regards Frank Oellien (EuCheMS DCC Secretary & EuCO-CC Chair) From owner-chemistry@ccl.net Tue Jun 2 22:57:00 2015 From: "Billy McCann thebillywayne[*]gmail.com" To: CCL Subject: CCL: Measuring Instantaneous Correlation of Individual Orbitals Message-Id: <-51421-150602220625-16989-P/1t6ITFX5s2wxuCNkbUoQ/./server.ccl.net> X-Original-From: Billy McCann Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Date: Tue, 2 Jun 2015 22:06:04 -0400 MIME-Version: 1.0 Sent to CCL by: Billy McCann [thebillywayne__gmail.com] I'd like to thank you all for your comments thus far. I'm realizing that some amount of rust has built up since my electronic structure theory class some years ago. Your responses, to the list and in private, have given me great material on which to reflect. My plan is to do some more thinking. Then I'll pester you guys some more. :) BW -- Billy Wayne McCann, Ph.D. http://bwayne.sdf.org irc://irc.freenode.net:bwayne "There is nothing new under the sun." ~ Solomon On Sun, May 31, 2015 at 10:58 PM, Susi Lehtola susi.lehtola[#]alumni.helsinki.fi wrote: > > Sent to CCL by: Susi Lehtola [susi.lehtola[#]alumni.helsinki.fi] > On 05/31/2015 08:16 AM, Billy McCann thebillywayne-,-gmail.com wrote: >> >> I'd like to, for now, leave aside density functional theory because I >> don't have much experience or insight into the nature of the >> exchange-correlation operators; I can't seem to get a systematic >> understanding of that particular operator in its various formulations. >> And it's this correlation energy which I'm curious about. That the >> operator contains both exchange, correlation, plus a correction to the >> kinetic energies of the Kohn-Sham orbitals confounds me even more when >> trying to understand it, not even mentioning double-hybrid DFA's. I >> know that brilliant scientists have worked on various density >> functional approximations, and I do not at all want to belittle their >> work. DFA is a great tools for physicists and chemists. > > > There is no "exchange-correlation operator"; exchange and correlation just > happen to be names that we call certain types of matrix elements of the > Coulomb operator. > > Now, DFT is nothing more exotic than the realization that one can exactly > write the Schrödinger equation as something that only depends on the > density, which yields a huge reduction in the degrees of freedom. The > problem is we don't know the exact functional, and there's no way to > approach the exact solution systematically. There's only a very rough > partitioning of the approximate functionals onto different levels of theory > (Jacob's ladder)... and going up in the ladder, for instance from GGA > functionals to hybrid GGA functionals, may give you much worse results. > >> If I understand correctly, all methods begin from the HF approximation and >> correct for >> dynamical correlation by making a linear combination of Slater >> determinants by different methods. > > > Yes, except for many-component wave functions like in MCSCF, where the > orbitals are optimized including some extent of (strong) correlation. > >> But what I'm wondering about is the correlation energy of a *single* >> atomic or molecular orbital. Is it that comparing the HF orbital >> energy to, say, a corresponding orbital resulting from a CCSD(T) >> calculation would yield such an energy? I've pondered this question, >> but I've read others who say that this isn't entirely the case because >> HF does indeed account for some small degree of electron correlation, >> but only in an averaged way. (I think I remember reading this in >> Cramer's text.) Perhaps MC-SCF may provide such an answer, by >> measuring the coefficients of each determinant? > > > Atomic or molecular orbitals aren't observables, so that notion doesn't make > sense. (Also, as already pointed out by Robert Molt, the notion of > correlation is also a bit ill defined. Richard Feynman said that instead of > correlation energy one should really talk about dumbness energy, since we > talk of correlation only because we're too dumb to solve the many-electron > Schrödinger equation directly.) > >> So my question is two-fold: >> >> 1. How can the dynamical electron correlation energy of a single >> atomic or molecular orbital be measured? Can it even be done? > > > You can't measure it. But in calculations you *can* define it by calculating > the difference E(full) - E(frozen orbital). This is, of course, often used > because the frozen core approximation is popular in post-HF calculations. > >> 2. Is it possible to make a generalized statement such as, "Core >> electrons experience a greater degree of correlation because they are >> surrounded by more electrons," or "Valence electrons experience a >> greater degree of electron correlation because they are bound more >> loosely to the system, allowing their wavefunctions to fluctuate more >> freely,"? > > > You'd need to separate strong and dynamic correlation. Strong correlation > only affects valence orbitals. For dynamic correlation IIRC both core and > valence orbitals usually have similar correlation energies, which is not > what one might expect. > > Namely, for core orbitals one can make the argument you gave above, that the > correlation energy should be larger than for valence electrons, because the > electron density is much larger in the core region. > > However, it is also true that the velocity of core orbitals is much higher > than of valence orbitals, so the electrons spend much less time in close > contact. > -- > ----------------------------------------------------------------------- > Mr. Susi Lehtola, PhD Chemist Postdoctoral Fellow > susi.lehtola#,#alumni.helsinki.fi Lawrence Berkeley National Laboratory > http://www.helsinki.fi/~jzlehtol USA > -----------------------------------------------------------------------http://www.ccl.net/chemistry/sub_unsub.shtmlConferences: > http://server.ccl.net/chemistry/announcements/conferences/> >