Jing Li, Ivan Duchemin, Xavier Blase, Valerio Olevano
SciPost Phys. 8, 020 (2020) ·
published 5 February 2020

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Since the '30s the interatomic potential of the beryllium dimer Be$_2$ has
been both an experimental and a theoretical challenge. Calculating the
groundstate correlation energy of Be$_2$ along its dissociation path is a
difficult problem for theory. We present ab initio manybody perturbation
theory calculations of the Be$_2$ interatomic potential using the GW
approximation and the BetheSalpeter equation (BSE). The groundstate
correlation energy is calculated by the trace formula with checks against the
adiabaticconnection fluctuationdissipation theorem formula. We show that
inclusion of GW corrections already improves the energy even at the level of
the randomphase approximation. At the level of the BSE on top of the GW
approximation, our calculation is in surprising agreement with the most
accurate theories and with experiment. It even reproduces an experimentally
observed flattening of the interatomic potential due to a delicate correlations
balance from a competition between covalent and van der Waals bonding.
Jing Li, N. D. Drummond, Peter Schuck, Valerio Olevano
SciPost Phys. 6, 040 (2019) ·
published 1 April 2019

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Over time, many different theories and approaches have been developed to
tackle the manybody problem in quantum chemistry, condensedmatter physics,
and nuclear physics. Here we use the helium atom, a real system rather than a
model, and we use the exact solution of its Schr\"odinger equation as a
benchmark for comparison between methods. We present new results beyond the
randomphase approximation (RPA) from a renormalized RPA (rRPA) in the
framework of the selfconsistent RPA (SCRPA) originally developed in nuclear
physics, and compare them with various other approaches like configuration
interaction (CI), quantum Monte Carlo (QMC), timedependent densityfunctional
theory (TDDFT), and the BetheSalpeter equation on top of the GW approximation.
Most of the calculations are consistently done on the same footing, e.g. using
the same basis set, in an effort for a most faithful comparison between
methods.
Dr Olevano: "In the following, if the journ..."
in Submission on Comparing manybody approaches against the helium atom exact solution by Jing Li, N. D. Drummond, Peter Schuck, Valerio Olevano