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Jul 092011
 
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Francesco Calcavecchia, Francesco Pederiva, and Thomas D. Kuehne

Institute of Physical Chemistry, Johannes Gutenberg-University Mainz, Staudinger Weg 9, D-55128 Mainz, Germany
Dipartimento di Fisica, University of Trento, via Sommerive 14, I-38050 Povo, Trento, Italy
Lawrence Livermore National Laboratory Livermore, California 94550, USA
Center for Computational Sciences, Johannes Gutenberg-University Mainz, Staudinger Weg 9, D-55128 Mainz, Germany

Journal of Unsolved Questions, 1, 2, Articles 13-18, 2011 (Received June 11th, accepted June 30th, published online July 9th 2011)

We present the Fermionic Shadow Wave Function in the context of variational quantum Monte Carlo for disordered systems. Using the example of liquid 3He it is demonstrated that this allows for very accurate calculations, but due to its sign problem only for small systems. For this reason two novel methods are proposed that in principle solve the associated sign problem, but do not allow for realistic simulations yet.

[download id=”22″]

Keywords: Fermionic Shadow Wave Function, Variational Monte Carlo

Dec 282010
 
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Leonie Anna Mueck, Johannes Gutenberg-University, Mainz, Germany

Journal of Unsolved Questions, 1, 1, Articles, 7-12, 2011 (Received December 10th, accepted December 27th, published online December 28th 2010)

The discovery of the first neutral compound with chemically bound argon HArF in 2000 was a sensation in noble gas chemistry. If HArF is interpreted as a donor- acceptor complex with H+ as an strong acceptor and F? as a donor fragment the question arises if light noble gases helium, neon and argon could also form donor- acceptor complexes with common Lewis acids and bases like AlF3 and NH3. A covalent interaction between a Lewis acid, a Lewis base and a noble gas could be achieved by spatially dividing the donor and acceptor fragment thus incorporating the donor-acceptor complex into a cage-like structure. Due to the small polarizability of the light noble gases the Lewis acidity and basicity of the employed donor and acceptor must be extremely high for the noble gas to react with the cage. Novel kinds of organic donors and acceptors were designed to fullfill these criteria. These novel donors and acceptors were included in organic cages that fix geometrical conditions to be most favourable for the formation of complexes with noble gases. Among the many considered cage-types were the particularly aesthetic egg-shaped fullerene-type cages and dragon-shaped cages. Despite their beauty and their conceptual originality, they did not meet the requirements of yielding a negative reaction energy with light noble gases but they may be useful for other purposes, e. g. as hosts for hydrogen molecules.

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Supporting information: [download id=”14″]

Keywords: Noble Gases, Donor-Acceptor Complexes, Computational Chemistry

Dec 082010
 
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Toru Shiozaki, University of Stuttgart, Germany

Journal of Unsolved Questions, 1, 1, Articles, 1-6 (2011) (Received November 14th, published online December 8th 2010)

Explicitly correlated F12 theories have been developed in the past decades to rectify the slow convergence

of dynamical electron correlation models with basis size, in which additional two-electron integrals over F12 kernels

are required. This article reviews some existing algorithms for these integrals, including the author’s attempt,

and leave an open question: what will be the most efficient algorithm (and who wants to implement it into a tightly

optimized code)?

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Keywords: theoretical chemistry, F12 methods, integral evaluation