Relativistic quantum chemistry: today and tomorrow

Liu, Wenjian

doi:10.1360/ssc-2020-0120

Cited by 14 publications

(15 citation statements)

References 38 publications

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“…which is composed of the kinetic energy operator T (nonrelativistic or relativistic 78,79 ), (static) nuclear attraction V nuc , Hartree potential V h , exact exchange potential Σ x , and XC potential V xc . The scaling coefficients c x and c xc denote the respective portions of Σ x and V xc included in the chosen hybrid functional.…”

Section: Tdksmentioning

confidence: 99%

Self-Adaptive Real-Time Time-Dependent Density Functional Theory for Core Excitations

Ye¹,

Wang²,

Zhang³

et al. 2022

Preprint

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Real-time time-dependent density functional theory (RT-TDDFT) can in principle access all excitations of a many-electron system exposed to a narrow pulse. However, this requires an accurate and efficient propagator for the numerical integration of the time-dependent Kohn-Sham equation. While a low-order time propagator is already sufficient for the low-lying valence excitations, it is no longer the case for the core excitations of systems even composed only of light elements, for which the use of a high-order propagator is indispensable. It is then crucial to choose a largest possible time step and a shortest possible simulation time, so as to reduce the computational cost. To this end, we propose here a robust AutoPST approach to determine automatically (Auto) the propagator (P), step (S), and time (T) for relativistic RT-TDDFT simulations of core excitations.J o u r n a l N a me , [ y e a r ] , [ v o l . ] ,

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Section: Tdksmentioning

confidence: 99%

Self-Adaptive Real-Time Time-Dependent Density Functional Theory for Core Excitations

Ye¹,

Wang²,

Zhang³

et al. 2022

Preprint

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“…As pointed out recently, , among the three components of electronic structure theory (i.e., relativity, correlation, and QED), it is correlation that is most challenging, especially for strongly correlated systems. Roughly speaking, a strongly correlated system features multiple open-shell orbitals or nearly degenerate electronic states thanks to the existence of a dense set of energetically adjacent frontier orbitals, such that there does not exist a single, leading component in the wave functions.…”

Section: Introductionmentioning

confidence: 99%

Further Development of iCIPT2 for Strongly Correlated Electrons

Zhang

Liu

Hoffmann

2021

J. Chem. Theory Comput.

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The efficiency of the recently proposed iCIPT2 [iterative configuration interaction (iCI) with selection and second-order perturbation theory (PT2); J. Chem. Theory Comput. 2020Comput. , 16, 2296 for strongly correlated electrons is further enhanced (by up to 20×) by using ( 1) a new ranking criterion for configuration selection, (2) a new particle-hole algorithm for Hamiltonian construction over randomly selected configuration state functions (CSF), and (3) a new data structure for the quick sorting of the variational and first-order interaction spaces. Meanwhile, the memory requirement is also significantly reduced. As a result, this improved implementation of iCIPT2 can handle 1 order of magnitude more CSFs than the previous version, as revealed by taking the chromium dimer and an iron−sulfur cluster, [Fe 2 S 2 (SCH 3 )] 4 2− , as examples.

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“…As the advent of the continuous and complete "Hamiltonian ladder" [5,6], the relativity problem in quantum chemistry can be regarded as solved, in the sense that one can just pick up the right Hamiltonian according to the target physics/chemistry and accuracy. In particular, all relativistic Hamiltonians [4,[7][8][9][10][11][12], including the effective QED [5,6,[13][14][15][16][17][18][19][20], can be written in the same second-quantized form…”

Section: Introductionmentioning

confidence: 99%

“…Even the 4C integral transformations can be made identical with the 2C ones if the quasi-4-component (Q4C) relativistic Hamiltonian [74,75] is adopted, which does not suffer from picture change errors [76] that otherwise plague all 2C relativistic Hamiltonians. Note also that the correlation contribution of negative energy states can readily be accounted for in both the 4C and 2C frameworks, so as to go beyond the no-pair approximation [5,6,14,[16][17][18][19][20]. As such, it is merely a matter of taste to work with 4C or 2C approaches.…”

Section: Introductionmentioning

confidence: 99%

SOiCI and iCISO: Combining iterative configuration interaction with spin-orbit coupling in two ways

Zhang,

Xiao,

Liu

2022

Preprint

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The near-exact iCIPT2 approach for strongly correlated systems of electrons, which stems from the combination of iterative configuration interaction (iCI, an exact solver of full CI) with configuration selection for static correlation and second-order perturbation theory (PT2) for dynamic correlation, is extended to the relativistic domain. In the spirit of spin separation, relativistic effects are treated in two steps: scalar relativity is treated by the infinite-order, spin-free part of the exact two-component (X2C) relativistic Hamiltonian, whereas spin-orbit coupling (SOC) is treated by the first-order, Douglas-Kroll-Hess-like SOC operator derived from the same X2C Hamiltonian. Two possible combinations of iCIPT2 with SOC are considered, i.e., SOiCI and iCISO. The former treats SOC and electron correlation on an equal footing, whereas the latter treats SOC in the spirit of state interaction, by constructing and diagonalizing an effective spin-orbit Hamiltonian matrix in a small number of correlated scalar states. Both double group and time reversal symmetries are incorporated to simplify the computation. Pilot applications reveal that SOiCI is very accurate for the spin-orbit splitting (SOS) of heavy atoms, whereas the computationally very cheap iCISO can safely be applied to the SOS of light atoms and even of systems containing heavy atoms when SOC is largely quenched by ligand fields.

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Relativistic quantum chemistry: today and tomorrow

Cited by 14 publications

References 38 publications

Self-Adaptive Real-Time Time-Dependent Density Functional Theory for Core Excitations

Self-Adaptive Real-Time Time-Dependent Density Functional Theory for Core Excitations

Further Development of iCIPT2 for Strongly Correlated Electrons

SOiCI and iCISO: Combining iterative configuration interaction with spin-orbit coupling in two ways

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