426 research outputs found
Convergence improvement for coupled cluster calculations
Convergence problems in coupled-cluster iterations are discussed, and a new
iteration scheme is proposed. Whereas the Jacobi method inverts only the
diagonal part of the large matrix of equation coefficients, we invert a matrix
which also includes a relatively small number of off-diagonal coefficients,
selected according to the excitation amplitudes undergoing the largest change
in the coupled cluster iteration. A test case shows that the new IPM (inversion
of partial matrix) method gives much better convergence than the
straightforward Jacobi-type scheme or such well-known convergence aids as the
reduced linear equations or direct inversion in iterative subspace methods.Comment: 7 pages, IOPP styl
Ba Quadrupole Polarizabilities: Theory versus Experiment
Three different measurements have been reported for the ground state
quadrupole polarizability in the singly ionized barium (Ba) which disagree
with each other. Our calculation of this quantity using the relativistic
coupled-cluster method disagrees with two of the experimental values and is
within the error bars of the other. We discuss the issues related to the
accuracy of our calculations and emphasize the need for further experiments to
measure the quadrupole polarizability for this state and/or the 5D states.Comment: 6 pages, 3 table
Relativistic multi-reference Fock-space coupled-cluster calculation of the forbidden 6s^2^1 S_0 \longrightarrow 6s5d^3 D_1 magnetic-dipole transition in ytterbium
We report the forbidden 6s^{2} ^{1}S_{0}\longrightarrow6s5d ^{3}D_{1}
magnetic-dipole transition amplitude computed using multi-reference Fock-space
coupled-cluster theory. Our computed transition matrix element
() is in excellent agreement with the experimental
value ( ). This value in combination with other
known quantities will be helpful to determine the parity non-conserving
amplitude for the 6s^{2} ^{1}S_{0}\longrightarrow6s5d ^{3}D_{1} transition in
atomic Yb. To our knowledge our calculation is the most accurate to date and
can be very important in the search of physics beyond the standard model. We
further report the and transition matrix elements which are
also in good agreement with the earlier theoretical estimates.Comment: Revtex, 4 EPS figure
Towards High Performance Relativistic Electronic Structure Modelling: The EXP-T Program Package
Modern challenges arising in the fields of theoretical and experimental
physics require new powerful tools for high-precision electronic structure
modelling; one of the most perspective tools is the relativistic Fock space
coupled cluster method (FS-RCC). Here we present a new extensible
implementation of the FS-RCC method designed for modern parallel computers. The
underlying theoretical model, algorithms and data structures are discussed. The
performance and scaling features of the implementation are analyzed. The
software developed allows to achieve a completely new level of accuracy for
prediction of properties of atoms and molecules containing heavy and superheavy
nuclei
On the performance of the intermediate Hamiltonian Fock-space coupled-cluster method on linear triatomic molecules: The electronic spectra of NpO2+, NpO22+, and Pu O22
International audienceIn this paper we explore the use of the novel relativistic intermediate Hamiltonian Fock-space coupled-cluster method in the calculation of the electronic spectrum for small actinyl ions (NpO2+, NpO22+, and PuO22+). It is established that the method, in combination with uncontracted double-zeta quality basis sets, yields excitation energies in good agreement with experimental values, and better than those obtained previously with other theoretical methods. We propose the reassignment of some of the peaks that were observed experimentally, and confirm other assignments
Configuration interaction calculation of hyperfine and P,T-odd constants on ^{207}PbO excited states for the electron EDM experiments
We report first configuration interaction calculations of hyperfine constants
A_\parallel and the effective electric field W_d acting on the electric dipole
moment of the electron, in two excited electronic states of ^{207}PbO. The
obtained hyperfine constants, A_\parallel = -3826 MHz for the a(1) state and
A_\parallel = 4887 MHz for the B(1) state, are in very good agreement with the
experimental data, -4113 MHz and 5000 \pm 200 MHz, respectively. We find W_d =
-(6.1 ^{+1.8}_{-0.6}) 10^{24} Hz/(e cm) for a(1), and W_d = (8.0 \pm 1.6)
10^{24} Hz/(e cm) for B(1). The obtained values are analyzed and compared to
recent relativistic coupled cluster results and a semiempirical estimate of W_d
for the a(1) state.Comment: 6 pages, REVTeX4 style, submitted to Pthys.Rev.
The electron electric dipole moment enhancement factors of Rubidium and Caesium atoms
The enhancement factors of the electric dipole moment (EDM) of the ground
states of two paramagnetic atoms; rubidium (Rb) and caesium (Cs) which are
sensitive to the electron EDM are computed using the relativistic
coupled-cluster theory and our results are compared with the available
calculations and measurements. The possibility of improving the limit for the
electron EDM using the results of our present work is pointed out.Comment: AISAMP7 Conference paper, Accepted in Journal of Physics: Conference
Series: 200
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