Computational Benchmarking for Ultrafast Electron Dynamics: Wave Function Methods vs Density Functional Theory.

Attosecond electron dynamics in small- and medium-sized molecules, induced by an ultrashort strong optical pulse, is studied computationally for a frozen nuclear geometry. The importance of exchange and correlation effects on the nonequilibrium electron dynamics induced by the interaction of the molecule with the strong optical pulse is analyzed by comparing the solution of the time-dependent Schrödinger equation based on the correlated field-free stationary electronic states computed with the equationof-motion coupled cluster singles and doubles and the complete active space multi-configurational self-consistent field methodologies on one hand, and various functionals in real-time time-dependent density functional theory (TDDFT) on the other. We aim to evaluate the performance of the latter approach, which is very widely used for nonlinear absorption processes and whose computational cost has a more favorable scaling with the system size.

New implementation of high-level correlated methods using a general block tensor library for high-performance electronic structure calculations.

This article presents an open-source object-oriented C++ library of classes and routines to perform tensor algebra.The primary purpose of the library is to enable post-Hartree–Fock electronic structure methods; however, the code is general enough to be applicable in other areas of physical and computational sciences. The library supports tensors of arbitrary order (dimensionality), size, and symmetry.

De-perturbative corrections for charge-stabilized double ionization potential equation-of-motion coupled-cluster method.

Charge stabilization improves the numeric performance of double ionization potential equation-of-motion (EOM-DIP) method when using unstable (autoionizing) dianion references. However, the stabilization potential introduces an undesirable perturbation to the target states' energies. Here we introduce and benchmark two approaches for removing the perturbation caused by the stabilization.

Using the charge-stabilization technique in the double ionization potential equation-of-motion calculations with dianion references.

The charge-stabilization method is applied to double ionization potential equation-of-motion (EOM-DIP) calculations to stabilize unstable dianion reference functions. The auto-ionizing character of the dianionic reference states spoils the numeric performance of EOM-DIP limiting applications of this method. We demonstrate that reliable excitation energies can be computed by EOM-DIP using a stabilized resonance wave function instead of the lowest energy solution corresponding to the neutral + free electron(s) state of the system.

Excited and ionized states of the ozone molecule with full triples coupled cluster methods.

The role of connected triple excitations in coupled cluster (CC) calculations of vertical excitation energies, ionization potentials, and the electron affinity of the ozone molecule is evaluated. The equation of motion (EOM) and Fock space (FS) multireference CC approaches with full triples have been used in the calculations. The effect of the T(3) and R(3) operators significantly improve the EOM CCSD results for all considered quantities.

Improving upon the accuracy for doubly excited states within the coupled cluster singles and doubles theory.

An alternative strategy of computations for double character excited states has been examined. The basic idea is to employ the reference function specific to the excited state of interest, as opposed to the traditionally used reference function, usually corresponding to the ground state, specific to the entire spectrum of a molecule. The procedure is used within the framework of the coupled cluster singles and doubles (CCSD) method.

Parallel implementation of the equation-of-motion coupled-cluster singles and doubles method and application for radical adducts of cytosine.

The equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) method has been implemented into the massively parallel ACES III program using two alternative strategies: (1) storing the entire EOM Hamiltonian matrix prior to diagonalization and (2) recomputing the four-virtual part of the matrix from integrals in a direct mode. The second is found to be far more efficient. EOM-CC shows virtually ideal scaling from 32 to 256 processors.

Ground state potential energy surfaces and bound states of M-He dimers (M=Cu,Ag,Au): a theoretical investigation.

We present an ab initio investigation on the ground state interaction potentials [potential energy surface (PES)] between helium and the group 11 metal atoms: copper, silver, and gold. To the best of our knowledge, there are no previous theoretical PESs proposed for Cu-He and Au-He, and a single one for Ag-He [Z. J.

Different equation-of-motion coupled cluster methods with different reference functions: the formyl radical.

The doublet and quartet excited states of the formyl radical have been studied by the equation-of-motion (EOM) coupled cluster (CC) method. The S(z) spin-conserving singles and doubles (EOM-EE-CCSD) and singles, doubles, and triples (EOM-EE-CCSDT) approaches, as well as the spin-flipped singles and doubles (EOM-SF-CCSD) method have been applied, subject to unrestricted Hartree-Fock (HF), restricted open-shell HF, and quasirestricted HF references. The structural parameters, vertical and adiabatic excitation energies, and harmonic vibrational frequencies have been calculated.