CCL: Case Studies of QM Computational Chemistry in Reactivity



 Sent to CCL by: =?iso-8859-1?Q?V=EDctor_Lua=F1a?= Cabal
 [victor%fluor.quimica.uniovi.es]
 On Fri, Sep 11, 2015 at 06:25:07AM -0400, Robert Molt
 r.molt.chemical.physics-*-gmail.com wrote:
 > Atomic charges, as a computational model, are an approximation which is
 > completely independent of DFT. No Nobel Prize has been given for atomic
 > charges (and never will be, because there is no such thing as the
 > quantum mechanical operator for atomic charge).
 To all,
 $
 Q = \int \rho(\bm{r}) d\bm{r}
   = \int \abs{\Psi}^2 d\bm{x}.
 $
 The quantum mechanical operator involved is \hat{1}. No problem
 with its definition or properties (analytic, hermitic, ...).
 The question of atomic charges is completely different and it is not
 related with the existence or not or an operator, but with the definition
 of the boundary of an atom in a molecule or solid. The problem is here
 $
 Q = \sum_i Q_i
   = \sum_i \int_{\Omega_i} rho(\bm{r}) d\bm{r}
 $
 What is $\Omega_i$? It is a problem of partitioning.
 Can we partition the bulk modulus of a crystal into ionic components?
 Elastic constants, energíes, multipolar moments, ...?  Yes, we and
 others did ... if you accept the QTAIM concepts. Can we partition any
 property? The QTAIM concepts assumes that, and there is a large school
 of people working on it.
 The e-mail by Stephan Grimme on this discussion mentioned clearly and
 appropriately the point. I believe in the QTAIM ideas, but they are
 not the only ones and they are not the ultimate and exclusive truth.
 So the sentence "there is no such thing as the quantum mechanical
 operator for atomic charge" is quite problematic and I can say with
 absolute property that "there is a perfectly defined operator of the
 atomic charge ... if you are studying an atom". And, believe me, there
 are also chemists studying atoms ... and solids ... and liquids ... and
 materials ... and ...
 So, please, calm down and do not jump to defend a person that is present
 in the discussiond and can defend his opinions by himself.
 Peace (Shalom, Salam, Paz, ...),
                                 Víctor Luaña
 --
      .  .    "In science a person can be convinced by a good argument.
     / `' \   That is almost impossible in politics or religion"
    /(o)(o)\  (Adapted from Carl Sagan)
   /`. \/ .'\  "Lo mediocre es peor que lo bueno, pero también es peor
  /   '`'`   \ que lo malo, porque la mediocridad no es un grado, es una
  |  \'`'`/  | actitud" -- Jorge Wasenberg, 2015
  |  |'`'`|  | (Mediocre is worse than good, but it is also worse than
   \/`'`'`'\/  bad, because mediocrity is not a grade, it is an attitude)
 ===(((==)))==================================+=========================
 ! Dr.Víctor Luaña, in silico chemist & prof. !"I have two
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 ! Departamento de Química Física y Analítica ! the urgent and the
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