Lucas Visscher - Academia.edu (original) (raw)

Papers by Lucas Visscher

Physical Chemistry Chemical Physics, 2011

The performance of the time-dependent density functional theory (TDDFT) approach has been evaluat... more The performance of the time-dependent density functional theory (TDDFT) approach has been evaluated for the electronic spectrum of the UO 2+ 2 , NUO + and NUN molecules. Different exchange-correlation functionals (LDA, PBE, BLYP, B3LYP, PBE0, M06, M06-L, M06-2X, CAM-B3LYP) and the SAOP model potential have been investigated, as has the relative importance of the adiabatic local density approximation (ALDA) to the exchange-correlation kernel. The vertical excitation energies have been compared with reference data obtained using accurate wave-function theory (WFT) methods.

The Journal of Chemical Physics

In the new field of quantum plasmonics, plasmonic excitations of silver and gold nanoparticles ar... more In the new field of quantum plasmonics, plasmonic excitations of silver and gold nanoparticles are utilized to manipulate and control light-matter interactions at the nanoscale. While quantum plasmons can be described with atomistic detail with Time-Dependent Density Functional Theory (TD-DFT) such studies are computationally challenging due to the size of the nanoparticles. An efficient alternative is to employ DFT without approximations only for the relatively fast ground state calculation and use tight-binding approximations in the demanding linear response calculations. In this work we use this approach to investigate the nature of plasmonic excitations under the variation of the separation distance between two nanoparticles. We thereby provide complementary characterizations of these excitations in terms of Kohn-Sham single-orbital transitions, intrinsic localized molecular fragment orbitals, scaling of the electron-electron interactions, and probability of electron tunneling between monomers.

The Journal of Chemical Physics

We report in this paper an implementation of 4-component relativistic Hamiltonian based Equation-... more We report in this paper an implementation of 4-component relativistic Hamiltonian based Equation-of-Motion Coupled-Cluster with singles and doubles (EOM-CCSD) theory for the calculation of ionization potential (IP), electron affinity (EA) and excitation energy (EE). In this work we utilize previously developed double group symmetry-based generalized tensor contraction scheme, and also extend it in order to carry out tensor contractions involving non-totally symmetric and odd-ranked tensors. Several approximated spin-free and two-component Hamiltonians can also be accessed in this implementation. We have applied this method to the halogen monoxide (XO, X= Cl, Br, I, At, Ts) species, in order to assess the quality of a few other recent EOM-CCSD implementations, where spin-orbit coupling contribution has been approximated in different degree. Besides, we also have studied various excited states of CH 2 IBr, CH 2 I 2 and I − 3 (as well as single electron attachment and detachment electronic states of the same species) where comparison has been made with a closely related multi-reference coupled-cluster method, namely Intermediate Hamiltonian Fock Space Coupled-Cluster singles and doubles (IHFS-CCSD) theory.

Physical Review A, Mar 23, 2012

The past few years have witnessed a remarkable interest in the application of quantum computing f... more The past few years have witnessed a remarkable interest in the application of quantum computing for solving problems in quantum chemistry more efficiently than classical computers allow. Very recently, proof-of-principle experimental realizations have been reported. However, so far only the nonrelativistic regime (i.e., the Schrödinger equation) has been explored, while it is well known that relativistic effects can be very important in chemistry. We present a quantum algorithm for relativistic computations of molecular energies. We show how to efficiently solve the eigenproblem of the Dirac-Coulomb Hamiltonian on a quantum computer and demonstrate the functionality of the proposed procedure by numerical simulations of computations of the spin-orbit splitting in the SbH molecule. Finally, we propose quantum circuits with three qubits and nine or ten controlled-not (cnot) gates, which implement a proof-of-principle relativistic quantum chemical calculation for this molecule and might...

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The Journal of Chemical Physics, 2014

$Research paper thumbnail of Relativistic general-order coupled-cluster method for high-precision calculations: Application to the Al^{+} atomic clock$

Journal of Computational Chemistry, 2011

Journal of Computational Chemistry, 2002

Journal of Computational Chemistry, 2013

Journal of Chemical Theory and Computation, 2013

Journal of Chemical Theory and Computation, 2009

Journal of Chemical Theory and Computation, 2010

Journal of Chemical Theory and Computation, 2014

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The Journal of Chemical Physics, 2000