Magnus expansion and in-medium similarity renormalization group
Abstract
We present an improved variant of the in-medium similarity renormalization group (IM-SRG) based on the Magnus expansion. In the new formulation, one solves flow equations for the anti-Hermitian operator that, upon exponentiation, yields the unitary transformation of the IM-SRG. The resulting flow equations can be solved using a first-order Euler method without any loss of accuracy, resulting in substantial memory savings and modest computational speedups. Since one obtains the unitary transformation directly, the transformation of additional operators beyond the Hamiltonian can be accomplished with little additional cost, in sharp contrast to the standard formulation of the IM-SRG. Ground state calculations of the homogeneous electron gas (HEG) and 16O nucleus are used as test beds to illustrate the efficacy of the Magnus expansion.
- Publication:
-
Physical Review C
- Pub Date:
- September 2015
- DOI:
- 10.1103/PhysRevC.92.034331
- arXiv:
- arXiv:1507.06725
- Bibcode:
- 2015PhRvC..92c4331M
- Keywords:
-
- 13.75.Cs;
- 21.30.Fe;
- 21.60.De;
- 27.20.+n;
- Nucleon-nucleon interactions;
- Forces in hadronic systems and effective interactions;
- Ab initio methods;
- 6<
- =A<
- =19;
- Nuclear Theory;
- Condensed Matter - Quantum Gases;
- Physics - Chemical Physics
- E-Print:
- 12 pages, 9 figures