Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Quantum mechanical calculation of the effects of stiff and rigid
  constraints in the conformational equilibrium of the Alanine dipeptide   If constraints are imposed on a macromolecule, two inequivalent classical
models may be used: the stiff and the rigid one. This work studies the effects
of such constraints on the Conformational Equilibrium Distribution (CED) of the
model dipeptide HCO-L-Ala-NH2 without any simplifying assumption. We use ab
initio Quantum Mechanics calculations including electron correlation at the MP2
level to describe the system, and we measure the conformational dependence of
all the correcting terms to the naive CED based in the Potential Energy Surface
(PES) that appear when the constraints are considered. These terms are related
to mass-metric tensors determinants and also occur in the Fixman's compensating
potential. We show that some of the corrections are non-negligible if one is
interested in the whole Ramachandran space. On the other hand, if only the
energetically lower region, containing the principal secondary structure
elements, is assumed to be relevant, then, all correcting terms may be
neglected up to peptides of considerable length. This is the first time, as far
as we know, that the analysis of the conformational dependence of these
correcting terms is performed in a relevant biomolecule with a realistic
potential energy function.

36
The categories of this paper are: cmp-lg
3
The categories of this paper are: physics
31
The categories of this paper are: ao-sci
8
The categories of this paper are: hep-ex
32
The categories of this paper are: atom-ph
21
The categories of this paper are: adap-org
14
The categories of this paper are: math-ph
16
The categories of this paper are: stat
1
The categories of this paper are: cs
15
The categories of this paper are: nucl-ex
27
The categories of this paper are: comp-gas
29
The categories of this paper are: funct-an
28
The categories of this paper are: alg-geom
24
The categories of this paper are: dg-ga
22
The categories of this paper are: chao-dyn
20
The categories of this paper are: acc-phys