Electronic excited-state wave functions for quantum Monte Carlo: Application to silane and methane

Porter, A. R.; Al-Mushadani, O. K.; Towler, M. D.; Needs, R. J.

doi:10.1063/1.1342765

Cited by 31 publications

(28 citation statements)

References 38 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The previous results for SiH 4 that are most comparable to our work are those of Porter et al 40 who carried out a DMC+ CPP calculation using the LDA bond length for SiH 4 . Their DMC+ CPP result of 9.47͑2͒ eV for the optical gap can be compared directly with our result of 8.93͑1͒ eV, i.e., a decrease in the gap of 0.5 eV in going from SiH 4 to GeH 4 .…”

Section: Cppsupporting

confidence: 87%

“…Porter et al 40 maintained, supporting earlier all-electron multireference single-and doubleexcitation configuration interaction ͑MRD-CI͒ work by Chantranupong et al, 69 that the first two peaks of the SiH 4 spectrum actually derive from a Jahn-Teller splitting of the triply degenerate t 2 → 4s transition, similar to the splitting in the photoelectron spectrum for the ionization energy. 68 ͑The excited state involves partially filled degenerate t 2 HOMO levels, which is subject to Jahn-Teller distortion that can break the T d symmetry and lift the degeneracy.͒ Thus the single calculated gap should be compared to the two experimental peaks, i.e., lie in between the two peaks, which is consistent with the calculated gaps for SiH 4 and GeH 4 .…”

Section: Cppmentioning

confidence: 60%

See 1 more Smart Citation

Quantum Monte Carlo calculations of the optical gaps of Ge nanoclusters using core-polarization potentials

2007

View full text Add to dashboard Cite

We report the results of a study of the ground-state and excitation energies of Ge atoms, molecules, and clusters as large as Ge 29 H 36 , using quantum Monte Carlo ͑QMC͒ for the valence electrons. QMC is one of the most accurate many-body methods; however, its accuracy is limited by the way the core is treated, which is especially important for atoms with shallow cores such as Ge. Here we treat the Ge core with a relativistic Hartree-Fock pseudopotential plus a core polarization potential ͑CPP͒ to take into account core-valence correlation at a many-body level. The CPP is found to be important for accurate calculations of the total energy, and for excitations of atoms and small molecules; however, there are only small changes in the lowest optical excitations of larger clusters, which can be understood in terms of the nature of the excitations. The results are compared with previous QMC calculations for the corresponding Si molecules and clusters. In addition, we find that QMC gaps are higher than those found in recent time-dependent density functional studies, by amounts similar to that previously found for Si systems.

show abstract

Section: Cppsupporting

confidence: 87%

Section: Cppmentioning

confidence: 60%

Quantum Monte Carlo calculations of the optical gaps of Ge nanoclusters using core-polarization potentials

2007

View full text Add to dashboard Cite

show abstract

“…The dotted and dot-dashed curves are the results of a RPA and a 45 All the results for the optical spectrum of small Na clusters are very similar, regardless of the exchange-correlation potential used. In contrast, hydrogenated silicon clusters show that a much better agreement with diffusion quantum Monte Carlo calculations (Grossman et al, 2001;Porter et al, 2001) and with experiments can be obtained when the exact exchange potential is used. FIG.…”

Section: The Exchange-correlation Kernel F XCmentioning

confidence: 93%

Electronic excitations: density-functional versus many-body Green’s-function approaches

2002

View full text Add to dashboard Cite

Electronic excitations lie at the origin of most of the commonly measured spectra. However, the first-principles computation of excited states requires a larger effort than ground-state calculations, which can be very efficiently carried out within density-functional theory. On the other hand, two theoretical and computational tools have come to prominence for the description of electronic excitations. One of them, many-body perturbation theory, is based on a set of Green's-function equations, starting with a one-electron propagator and considering the electron-hole Green's function for the response. Key ingredients are the electron's self-energy ⌺ and the electron-hole interaction. A good approximation for ⌺ is obtained with Hedin's GW approach, using density-functional theory as a zero-order solution. First-principles GW calculations for real systems have been successfully carried out since the 1980s. Similarly, the electron-hole interaction is well described by the Bethe-Salpeter equation, via a functional derivative of ⌺. An alternative approach to calculating electronic excitations is the time-dependent density-functional theory (TDDFT), which offers the important practical advantage of a dependence on density rather than on multivariable Green's functions. This approach leads to a screening equation similar to the Bethe-Salpeter one, but with a two-point, rather than a four-point, interaction kernel. At present, the simple adiabatic local-density approximation has given promising results for finite systems, but has significant deficiencies in the description of absorption spectra in solids, leading to wrong excitation energies, the absence of bound excitonic states, and appreciable distortions of the spectral line shapes. The search for improved TDDFT potentials and kernels is hence a subject of increasing interest. It can be addressed within the framework of many-body perturbation theory: in fact, both the Green's functions and the TDDFT approaches profit from mutual insight. This review compares the theoretical and practical aspects of the two approaches and their specific numerical implementations, and presents an overview of accomplishments and work in progress. CONTENTS

show abstract

“…[70] for general aspects of multireference perturbation theory [MRPT]), the complete active space valence bond (CASVB) method, [71] the symmetry-adapted cluster configuration interaction (SAC-CI) method, [72] and quantum Monte Carlo methods for excited states. [73,74] Moreover, an application of the density-matrix renormalization group (DMRG) algorithm to excited states of the carotenoid b-carotene has been reported. [75] The focus of most developments for excited states is on accurate excitation energies.…”

Section: Theoretical Methods For Excited Statesmentioning

confidence: 99%

Quantum Chemical Description of Absorption Properties and Excited‐State Processes in Photosynthetic Systems

2011

View full text Add to dashboard Cite

The theoretical description of the initial steps in photosynthesis has gained increasing importance over the past few years. This is caused by more and more structural data becoming available for light-harvesting complexes and reaction centers which form the basis for atomistic calculations and by the progress made in the development of first-principles methods for excited electronic states of large molecules. In this Review, we discuss the advantages and pitfalls of theoretical methods applicable to photosynthetic pigments. Besides methodological aspects of excited-state electronic-structure methods, studies on chlorophyll-type and carotenoid-like molecules are discussed. We also address the concepts of exciton coupling and excitation-energy transfer (EET) and compare the different theoretical methods for the calculation of EET coupling constants. Applications to photosynthetic light-harvesting complexes and reaction centers based on such models are also analyzed.

show abstract

Electronic excited-state wave functions for quantum Monte Carlo: Application to silane and methane

Cited by 31 publications

References 38 publications

Quantum Monte Carlo calculations of the optical gaps of Ge nanoclusters using core-polarization potentials

Quantum Monte Carlo calculations of the optical gaps of Ge nanoclusters using core-polarization potentials

Electronic excitations: density-functional versus many-body Green’s-function approaches

Quantum Chemical Description of Absorption Properties and Excited‐State Processes in Photosynthetic Systems

Contact Info

Product

Resources

About