Dear Prof. Artacho With all my respect, what you say holds true if you construct a energy surface for the nuclei movement E_KS(R), where R are generalized atomic positions. But that is not strictly the case I was thinking about. I was thinking in a given E_KS calculated for a given atomic position. In this sense the quantity E_KS, in my opinion is not a potential strictly speaking, but the sum of the electronic kinetic and potential energies for a fixed external potential.
>From what Andres say - if I'm not interpreting something very wrong - it seems to me that the value E_KS itself, for a given atomic configuration, could be interpreted as a potential. Although that is absolutely true if the energy surface for the atomic movements is constructed - as you well mentioned - in my opinion this concept cannot be easily extrapolated for a single point energy, because E_KS is not the potential it self, but a discrete points in the nuclear potential function ( what I called E_KS(R) above ). That is what I meant. Sorry if it seemed rough. With my best regards Ney On Fri, Feb 18, 2011 at 6:08 PM, Emilio Artacho <[email protected]> wrote: > Ney > > E_KS is the total energy of the electron system for each nuclear snapshot. > The total energy (pot+kin) of > the electrons represents the effective potential energy for the nuclear > dynamics, in the adiabatic > decomposition of both dynamics. It is thus the relevant potential energy > surface for the nuclear > dynamics, hence the name (I don't think it is misleading). > > (the springs etc of the mentioned examples are model descriptions of how > this total energy of > the electrons would change with nuclear positions: > the empirically parametrised atomic *potentials* in > empirical MD) > > It is Born-Oppenheimer, as Andres was saying. > > Emilio > > > > On Feb 18 2011, N H wrote: > > In molecular dynamics all chemical bonds are represents - I mean >> represented - by springs ... so it is obvoious that what dou you have in the >> and is a potential energy! But that is not true if if you are comparing >> quantum levels ... it doesn't matter if HF, CI or KS ones - because in this >> energies what you have are components of the electronic kinetic energy plus >> all the potential terms. And by potentiual terms I mean the electrostatic >> interactions of the electrosn with their couter parts in the system plus the >> interactions with the external field! >> >> In this sense ... calling the E_KS energy as the "potential energy" is >> simply misleading! >> >> Cheers >> >> Ney >> > > > -- > 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 > >
