12 research outputs found
Generalized relativistic small-core pseudopotentials accounting for quantum electrodynamic effects: construction and pilot applications
A simple procedure to incorporate one-loop quantum electrodynamic (QED)
corrections into the generalized (Gatchina) nonlocal shape-consistent
relativistic pseudopotential model is described. The pseudopotentials for Lu,
Tl, and Ra replacing only inner core shells (with principal quantum numbers
for the two former elements and for the latter one) are
derived from the solutions of reference atomic SCF problems with the
Dirac-Coulomb-Breit Hamiltonian to which the model Lamb shift operator added.
QED contributions to atomic valence excitation energies evaluated at the SCF
level are demonstrated to exceed the errors introduced by the pseudopotential
approximation itself by an order of magnitude. Pilot applications of the new
model to calculations of excitation energies of two-valence-electron atomic
systems using the intermediate-Hamiltonian relativistic Fock space coupled
cluster method reformulated here for incomplete main model spaces are reported.
Implications for high-accuracy molecular excited state calculations are
discussed
Which oxidation state of uranium and thorium as point defects in xenotime is favorable?
Relativistic study of xenotime, YPO, containing atoms thorium and uranium
as point defects is performed in the framework of cluster model with using the
compound-tunable embedding potential (CTEP) method proposed by us recently. The
Y-(PO)-Y'-O' cluster for xenotime is considered, in
which central part, [Y-(PO)], is the main cluster, whereas
outermost 22 atoms of yttrium and 104 atoms of oxygen are treated as its
environment and compose electron-free CTEP with the total charge of . The
P and O atoms of the orthophosphate groups nearest to the central Y atom are
treated at all-electron level. The central Y, its substitutes, Th and U,
together with environmental Y atoms are described within different versions of
the generalized relativistic pseudopotential method. Correctness of our cluster
and CTEP models, constructed in the paper, is justified by comparing the Y-O
and P-O bond lengths with corresponding periodic structure values of the \ypo4
crystal, both experimental and theoretical. Using this cluster model, chemical
properties of solitary point defects, X = U, Th, in xenotime are analyzed. It
has been shown that the oxidation state is energetically more profitable
than not only for thorium but for uranium as well (
eV) despite the notably higher ionic radius of U compared to Y,
whereas ionic radii of U and Y are close. This leads to notable
local deformation of crystal geometry around the U impurity in xenotime
and contradicts to widespread opinion about favorite oxidation state of uranium
in such kind of minerals.Comment: 8 pages, 4 figures, 3 table
Compound-tunable embedding potential method to model local electronic excitations on -element ions in solids: Pilot relativistic coupled cluster study of Ce and Th impurities in yttrium orthophosphate, YPO
A method to simulate local properties and processes in crystals with
impurities via constructing cluster models within the frame of the
compound-tunable embedding potential (CTEP) and highly-accurate {\it ab initio}
relativistic molecular-type electronic structure calculations is developed and
applied to the Ce and Th-doped yttrium orthophosphate crystals, YPO, having
xenotime structure. Two embedded cluster models are considered, the "minimal"
one, YO@CTEP, consisting of the central Y cation and its
first coordination sphere of eight O anions (i.~e.\ with broken P--O
bonds), and its extended counterpart, Y(PO)@CTEP, implying
the full treatment of all atoms of the PO anions nearest to the
central Y cation. CTEP denote here the corresponding
cluster environment described within the CTEP method. The relativistic
Fock-space coupled cluster (FS RCC) theory is applied to the minimal cluster
model to study electronic excitations localized on Ce and Th
impurity ions. Calculated transition energies for the cerium-doped xenotime are
in a good agreement with the available experimental data (mean absolute
deviation of ca.0.3 eV for type transitions). For the thorium-doped
crystal the picture of electronic states is predicted to be quite complicated,
the ground state is expected to be of the character. The uncertainty for
the excitation energies of thorium-doped xenotime is estimated to be within
0.35 eV. Radiative lifetimes of excited states are calculated at the FS RCC
level for both doped crystals. The calculated lifetime of the lowest state
of Ce differs from the experimentally measured one by no more than
twice
Broadband velocity modulation spectroscopy of HfF^+: towards a measurement of the electron electric dipole moment
Precision spectroscopy of trapped HfF^+ will be used in a search for the
permanent electric dipole moment of the electron (eEDM). While this dipole
moment has yet to be observed, various extensions to the standard model of
particle physics (such as supersymmetry) predict values that are close to the
current limit. We present extensive survey spectroscopy of 19 bands covering
nearly 5000 cm^(-1) using both frequency-comb and single-frequency laser
velocity-modulation spectroscopy. We obtain high-precision rovibrational
constants for eight electronic states including those that will be necessary
for state preparation and readout in an actual eEDM experiment.Comment: 13 pages, 7 figures, 3 table
RELATIVISTIC COMBINED PSEUDOPOTENTIALRESTORATION METHOD FOR STUDYING MULTITUDE OF PROPERTIES IN HEAVY-ATOM SYSTEMS
This work is supported by the RFBR Grant No. 09--03--01034.Author Institution: B.P.Konstantinov Petersburg Nuclear Physics Institute, Gatchina; Leningrad district 188300, RussiaThe relativistic pseudopotential (RPP) calculations of valence (spectroscopic, chemical etc.) properties of molecules are very efficient because the modern two-component RPP methods allows one to treat very accurately the correlation and relativistic effects for the valence electrons of a molecule and to reduce dramatically the computational cost. The valence molecular spinors are usually smoothed in atomic cores and, as a result, direct calculation of electronic densities near heavy nuclei within such approach directly is impossible. Precise calculations of such properties, as hyperfine constants and other magnetic properties, parity nonconservation effects, which are described by the operators heavily concentrated in atomic cores, usually require very accurate accounting for both relativistic and correlation effects. Electronic structure should be well evaluated in both valence and atomic core regions. However, precise all-electron four-component treatment of molecules with heavy elements is yet rather consuming. In the report, an alternative approach based on the RPP method and one-center core-restoration technique [1] developed by the authors for such studies is discussed. Its efficiency is illustrated in benchmark to-date calculations of magneticdipole and electric quadrupole hyperfinestructure constants, as well as the space parity (P) and time-reversal symmetry (T) nonconservation effects in polar heavy-atom molecules, including HfF, PtH, ThO and WC, which are studied now as promising candidates for the experimental search of the electron electric dipole moment (eEDM). \vspace{5mm} [1] A.V.Titov, N.S.Mosyagin, A.N.Petrov, T.A.Isaev, D.DeMille, Progr.\ Theor.\ Chem.\ Phys., {\bf 15B}, 253 (2006)
LIBGRPP: A Library for the Evaluation of Molecular Integrals of the Generalized Relativistic Pseudopotential Operator over Gaussian Functions
Generalized relativistic pseudopotentials (GRPP) of atomic cores implying the use of different potentials for atomic electronic shells with different principal quantum numbers give rise to accurate and reliable relativistic electronic structure models of atoms, molecules, clusters, and solids. These models readily incorporate the effects of Breit electron–electron interactions and one-loop quantum electrodynamics effects. Here, we report the computational procedure for evaluating one-electron integrals of GRPP over contracted Gaussian functions. This procedure was implemented in a library of routines named LIBGRPP, which can be integrated into existing quantum chemistry software, thus enabling the application of various methods to solve the many-electron problem with GRPPs. Pilot applications to electronic transitions in the ThO and UO2 molecules using the new library and intermediate-Hamiltonian Fock space relativistic coupled cluster method are presented. Deviations of excitation energies obtained within the GRPP approach from their all-electron Dirac–Coulomb–Gaunt counterparts do not exceed 50 cm−1 for the 31 lowest-energy states of ThO and 110 cm−1 for the 79 states of UO2. The results clearly demonstrate that rather economical tiny-core GRPP models can exceed in accuracy relativistic all-electron models defined by Dirac–Coulomb and Dirac–Coulomb–Gaunt Hamiltonians
Ab initio study of electronic states and radiative properties of the AcF molecule
Relativistic coupled-cluster calculations of the ionization potential, dissociation energy, and excited electronic states under 35 000 cm−1 are presented for the actinium monofluoride (AcF) molecule. The ionization potential is calculated to be IPe = 48 866 cm−1, and the ground state is confirmed to be a closed-shell singlet and thus strongly sensitive to the T,P-violating nuclear Schiff moment of the Ac nucleus. Radiative properties and transition dipole moments from the ground state are identified for several excited states, achieving a mean uncertainty estimate of ∼450 cm−1 for the excitation energies. For higher-lying states that are not directly accessible from the ground state, possible two-step excitation pathways are proposed. The calculated branching ratios and Franck–Condon factors are used to investigate the suitability of AcF for direct laser cooling. The lifetime of the metastable (1)3Δ1 state, which can be used in experimental searches of the electric dipole moment of the electron, is estimated to be of order 1 ms
Ab initio study of electronic states and radiative properties of the AcF molecule
Relativistic coupled-cluster calculations of the ionization potential,
dissociation energy, and excited electronic states under 35,000 cm are
presented for the actinium monofluoride (AcF) molecule. The ionization
potential is calculated to be IP cm, and the ground state is
confirmed to be a closed-shell singlet and thus strongly sensitive to the
,-violating nuclear Schiff moment of the Ac nucleus.
Radiative properties and transition dipole moments from the ground state are
identified for several excited states, achieving an uncertainty of 450
cm for the excitation energies. For higher-lying states that are not
directly accessible from the ground state, possible two-step excitation
pathways are proposed. The calculated branching ratios and Franck-Condon
factors are used to investigate the suitability of AcF for direct laser
cooling. The lifetime of the metastable state, which can be
used in experimental searches of the electric dipole moment of the electron, is
estimated to be of order 1 ms