Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Assessment of two hybrid van der Waals density functionals for covalent
  and non-covalent binding of molecules   Two hybrid van der Waals density functionals (vdW-DFs) are constructed using
25%, Fock exchange with i) the consistent-exchange vdW-DF-cx functional and ii)
with the vdW-DF2 functional. The ability to describe covalent and non-covalent
binding properties of molecules are assessed. For properties related to
covalent binding, atomization energies (G2-1 set), molecular reaction energies
(G2RC set), as well as ionization energies (G21IP set) are benchmarked against
experimental reference values. We find that hybrid-vdW-DF-cx yields results
that are rather similar to those of the standard non-empirical hybrid PBE0 [JCP
110, 6158 (1996)]. Hybrid vdW-DF2 follows somewhat different trends, showing on
average significantly larger deviations from the reference energies, with a MAD
of 14.5 kcal/mol for the G2-1 set. Non-covalent binding properties of molecules
are assessed using the S22 benchmark set of non-covalently bonded dimers and
the X40 set of dimers of small halogenated molecules, using wavefunction-based
quantum chemistry results for references. For the S22 set, hybrid-vdW-DF-cx
performs better than standard vdW-DF-cx for the mostly hydrogen-bonded systems.
Hybrid-vdW-DF2 offers a slight improvement over standard vdW-DF2. Similar
trends are found for the X40 set, with hybrid-vdW-DF-cx performing particularly
well for binding involving the strongly polar hydrogen halides, but poorly for
systems with tiny binding energies. Our study of the X40 set reveals both the
potential of mixing Fock exchange with vdW-DF, but also highlights shortcomings
of the hybrids constructed here. The solid performance of hybrid-vdW-DF-cx for
covalent-bonded systems, as well as the strengths and issues uncovered for
non-covalently bonded systems, makes this study a good starting point for
developing even more precise hybrid vdW-DFs.

24
The categories of this paper are: dg-ga
36
The categories of this paper are: cmp-lg
27
The categories of this paper are: comp-gas
1
The categories of this paper are: cs
14
The categories of this paper are: math-ph
13
The categories of this paper are: quant-ph
33
The categories of this paper are: plasm-ph
28
The categories of this paper are: alg-geom
31
The categories of this paper are: ao-sci
32
The categories of this paper are: atom-ph
12
The categories of this paper are: nucl-th
2
The categories of this paper are: math
10
The categories of this paper are: q-bio
11
The categories of this paper are: hep-lat
22
The categories of this paper are: chao-dyn
6
The categories of this paper are: astro-ph