arXiv subjects

Charlotte Rickert

Publications and source records attributed to Charlotte Rickert.

3 recordsLinked to original sources

arXiv2026

ElemCo.jl: A Julia package for electron-correlation methods

We present ElemCo.jl, an open-source Julia package for molecular electronic structure and properties calculations with a particular emphasis on Coupled Cluster and Distinguishable Cluster methods. The package provides a high-level, macro-based user interface which makes routine calculations accessible to users with no prior Julia experience. A newly developed visualizer, JLmol, assists in the graphical preparation of ElemCo.jl input files and displays results such as molecular orbitals. ElemCo.jl offers restricted closed-shell and unrestricted variants of state-of-the-art electron-correlation methods such as FCI, MP2, CCSD(T) as well as EOM-CCSD and the DC methods DCSD and DC-CCSDT. In addition to traditional approaches, ElemCo.jl provides recently developed methods that are currently unique to the package. These include tensor-decomposed implementations of DCSD and DC-CCSDT (SVD-DCSD and SVD-DC-CCSDT) as well as two-determinant and fixed-reference CC and DC methods. For excited-state calculations, ElemCo.jl also offers EOM-DCSD, which is benchmarked in this work against CC3 on the QUEST3 benchmark set, alongside EOM-CCSD. Furthermore, both ground and excited states, including those of multireference character, can be treated using CIPHI - an efficient selected Configuration Interaction (CI) approach employing a CIPSI/Heat-Bath-CI-based algorithm. Users can directly invoke internal functions from the input file, enabling them to test and compose new methods without the need to modify ElemCo.jl's source code. Also, ElemCo.jl can be readily interfaced with external quantum chemistry codes through the Fcidump format, for example as the high-level solver for transcorrelated Hamiltonians, periodic embedded fragments, etc. We provide a detailed overview of ElemCo.jl's methodological repertoire and discuss its technical details and implementation, performance, interfaces, and usage.

physics.chem-ph↗

arXiv2026

Application of the aperiodic defect model to a negatively charged monovacancy in phosphorene

We apply the recently introduced aperiodic defect model (ADM) to a negatively charged monovacancy in a phosphorene monolayer. In contrast to conventional supercell approaches, the ADM treats a single defect embedded in the true non-defective crystalline mean field thereby avoiding spurious defect-defect interactions and the need for charge corrections. At the same time, it effectively reduces the calculation to a fragment, enabling the use of high-level molecular electronic-structure methods. Converging the Hartree-Fock and correlation contributions to the thermodynamic limit yields a benchmark CCSD(T)/POB-TZVP-rev2 formation energy of 0.81 eV for the negatively charged monovacancy in the (5|9) configuration. The excitation energy to the lowest singlet excited state of this defect at the EOM-CCSD/POB-TZVP-rev2 level is found to be 1.95 eV. Overall, the ADM provides a highly promising route towards quantitatively accurate and systematically improvable descriptions of defects in solids and on surfaces, bridging the gap between solid-state physics and molecular quantum chemistry.

physics.chem-ph↗

arXiv2024

Tensor Decomposed Distinguishable Cluster. I. Triples Decomposition

We present a cost-reduced approach for the distinguishable cluster approximation to coupled cluster with singles, doubles and iterative triples (DC-CCSDT) based on a tensor decomposition of the triples amplitudes. The triples amplitudes and residuals are processed in the singular-value-decomposition (SVD) basis. Truncation of the SVD basis according to the values of the singular values together with the density fitting (or Cholesky) factorization of the electron repulsion integrals reduces the scaling of the method to $N^6$, and the DC approximation removes the most expensive terms of the SVD triples residuals and at the same time improves the accuracy of the method. The SVD basis vectors for the triples are obtained from the approximate CC3 triples density matrices constructed in an intermediate SVD basis of doubles amplitudes. This allows us to avoid steps that scale higher than $N^6$ altogether. Tests against DC-CCSDT and CCSDT(Q) on a benchmark set of chemical reactions with closed-shell molecules demonstrate that the SVD-error is very small already with moderate truncation thresholds, especially so when using a CCSD(T) energy correction. Tests on alkane chains demonstrated that the SVD-error grows linearly with system size confirming the size extensivity of SVD-DC-CCSDT within a chosen truncation threshold.

physics.chem-ph↗