Numerical Atomic Basis Set Research Articles

Interpolative Separable Density Fitting Decomposition for Accelerating Hartree-Fock Exchange Calculations within Numerical Atomic Orbitals.

The high cost associated with the evaluation of Hartree-Fock exchange (HFX) makes hybrid functionals computationally challenging for large systems. In this work, we present an efficient way to accelerate HFX calculations with numerical atomic basis sets. Our approach is based on the recently proposed interpolative separable density fitting (ISDF) decomposition to construct a low-rank approximation of the HFX matrix, which avoids explicit calculations of the electron repulsion integrals (ERIs) and significantly reduces the computational cost. We implement the ISDF method for hybrid functional (PBE0) calculations in the HONPAS package. We take benzene and polycyclic aromatic hydrocarbon molecules as examples and demonstrate that hybrid functionals with ISDF yield quite promising results at a significantly reduced computational cost. Especially, the ISDF approach reduces the total cost of the evaluating HFX matrix by nearly 2 orders of magnitude compared to conventional approaches of direct evaluation of ERIs.

How does the porphyrin-like vacancy affect the spectral properties of graphene quantum dots? A theoretical study

By processing graphene quantum dot, an ideal semiconductor material with suitable band gap and higher electron mobility can be obtained. Thus, it has a broad prospect in the application of photoelectric response materials. Here, a graphene defect with porphyrin-like structure is selected to achieve the controlable light absorption. The double five-membered-ring parallel vacancy are based on self-healing properties of popular graphene defects. Aimed to separate exciton and hole more effectively and achieve higher photoelectric conversion efficiency, the occupied orbital and unoccupied orbital of the quantum dot with objected defect structure is taken as orderly dispersion to form an obvious charge separation state under the demonstration with first principles calculation. Most importantly, a real time real space charge separation is calculated by time-dependent ab-initio quantum dynamics based on numerical atomic basis sets. The result shows the specific graphene defects can form an efficient pure graphene photoelectric response medium like porphyrin skeleton, and the vacancy will induce to adjust and control the specific wavelength of the response light and charge separated state manipulably with odevity of number of peripheral carbon rings by the calculation of ultrafast process.

Large-scale ab initio simulations based on systematically improvable atomic basis

We present a first-principles computer code package (ABACUS) that is based on density functional theory and numerical atomic basis sets. Theoretical foundations and numerical techniques used in the code are described, with focus on the accuracy and transferability of the hierarchical atomic basis sets as generated using a scheme proposed by Chen et al. (2010). Benchmark results are presented for a variety of systems include molecules, solids, surfaces, and defects. All results show that the ABACUS package with its associated atomic basis sets is an efficient and reliable tool for simulating both small and large-scale materials.

Structural evolution study of 1−2 nm gold clusters

We have explored lowest energy minima structures of gold atom clusters both, charged and neutral (Au\hbox{$_{n}^{\nu}$}νn with n = 20, 28, 34, 38, 55, 75, 101, 146, 147, 192, 212 atoms and ν = 0, ±1). The structures have been obtained from first principles generalized gradient approximation, density functional theory (DFT) calculations based on norm-conserving pseudopotentials and numerical atomic basis sets. We have found two new disordered or defective isomers lower in energy than their ordered counterparts for n = 101, 147. The purpose of this work is to systematically study the difference between the electronic properties of the two lowest ordered and disordered isomers for each size. Our results agree with previous first principle calculations and with some recent experimental results (Au20 and Au101). For each case we report total energies, binding energies, ionization potentials, electron affinities, density of states, highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps, Housdorff chirality measure index and their simulated image in a high resolution transmission electron microscopy (HRTEM). The calculated properties of the two low lying (ordered and disordered) isomers show clear differences as to be singled out in a suitable experimental setting. An extensive discussion on the evolution with size of the cohesive energy, the ionization potentials, the electron affinities, the HOMO-LUMO gaps and their index of chirality to determine the crossover between them is given.

Linear scaling electronic structure calculations with numerical atomic basis set

We discuss in this review recent progress, especially by our group, on linear scaling algorithms for electronic structure calculations with numerical atomic basis sets. The principles of the construction of numerical basis sets and the Hamiltonian are introduced first. Then we discuss how to solve the single-electron equation self-consistently, and how to obtain electronic properties via post-self-consistent-field processes in a linear scaling way. The linear response calculation with linear scaling is also introduced. Numerical implementation is emphasized, with some applications presented for demonstration purposes.

Structural and electronic properties of Ce nO 2n ( n = 1–5) nanoparticles: A computational study

Understanding the electronic structures and properties of different size CeO 2 nanoparticles is very important for further application in the field of catalysis used in several promising materials. In this study, we have elucidated the electronic analyses of (CeO 2) n ( n = 1–5) nanoparticles through first-principle density-functional theory approach. All structures with the global minimal energies are obtained by fire algorithm combining simulated annealing method and then are further re-optimized by DMol 3 program with double numerical atomic basis sets. Two useful analyzed methods (Fukui function and electronic density of state) are calculated to explain the chemical reactivity of different sites for (CeO 2) n ( n = 1–5) nanoparticles.

Trends in the structure and bonding of neutral and charged noble metal clusters

AbstractWe present a systematic study of the electronic and geometric structure of neutral and charged noble metal clusters X (X = Cu, Ag, Au; n ≤ 13; ν = –1,0,+1), obtained from first principles GGA density functional calculations based on norm‐conserving pseudopotentials and a numerical atomic basis set. We determined that the maximum number of atoms forming planar structures with charge ν = (–1,0,+1) are (12, 11, 7) for gold, (5, 6, 5) for silver, and (5, 6, 4) for copper clusters. These results are compared with previous experimental and theoretical estimates. We argue that the tendency to planarity of gold clusters, which is much larger than in copper and silver, is strongly favored by relativistic effects, which decrease the s‐d electron promotion energy and lead to hybridization of the half‐filled 6s orbital with the occupied 5dz2 orbital. Trends for the calculated cohesive energy, average bond lengths, hardness (ionization potential minus electron affinity), and fragmentation energy of the X cluster are presented and discussed in comparison with available experiments and other calculations. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005

Trends in the structure and bonding of noble metal clusters

We present a systematic study of the electronic properties and the geometric structure of noble metal clusters ${X}_{n}^{\ensuremath{\nu}}$ ($X=\mathrm{Cu}$, Ag, Au; $\ensuremath{\nu}=\ensuremath{-}1,0,+1$; $n\ensuremath{\leqslant}13$ and $n=20$), obtained from first-principles generalized gradient approximation density functional calculations based on norm-conserving pseudopotentials and numerical atomic basis sets. We obtain planar structures for the ground state of anionic $(\ensuremath{\nu}=\ensuremath{-}1)$, neutral $(\ensuremath{\nu}=0)$, and cationic $(\ensuremath{\nu}=1)$ species of gold clusters with up to 12, 11, and 7 atoms, respectively. In contrast, the maximum size of planar clusters with $\ensuremath{\nu}=\ensuremath{-}1,0,+1$ are $n=(5,6,5)$ for silver and (5,6,4) for copper. For ${X}_{20}$ we find a ${T}_{d}$ symmetry for gold and a compact ${C}_{s}$ structure for silver and copper. Our results for the cluster geometries agree partially with previous first-principles calculations, and they are in good agreement with recent experimental results for anionic and cationic gold clusters. The tendency to planarity of gold clusters, which is much larger than in copper and silver, is strongly favored by relativistic effects, which decrease the $s\text{\ensuremath{-}}d$ promotion energy and lead to hybridization of the half-filled $6s$ orbital with the fully occupied $5{d}_{{z}^{2}}$ orbital. That picture is substantiated by analyzing our calculated density matrix for planar and three-dimensional clusters of gold and copper. The trends for the cohesive energy, ionization potentials, electron affinities, and highest accupied and lowest unoccupied molecular orbital gap, as the cluster size increases, are studied in detail for each noble metal and rationalized in terms of two- and three-dimensional electronic shell models. The most probable fragmentation channels for ${X}_{n}^{\ensuremath{\nu}}$ clusters are in very good agreement with available experiments.

Study of (Al2O3)n(Ox) clusters with n ? 16 and x = 0, 1, 2 from first principles calculations

The ionic and electronic structure of (Al2O3)n(Ox) clusters with n ≤ 16 and x = 0, 1, 2 is studied by means of first principles density functional calculations, norm-conserving pseudopotentials and a numerical atomic basis set. The equilibrium geometries have been determined by total energy minimization, starting with several initial geometries for each cluster size. The trends obtained for the atomic arrangements (structural isomers, coordination numbers, “disordered” versus ”ordered” structures, etc.) and the electronic properties (binding energies, Homo-Lumo gap and dipole moments) are discussed. For most of the oxidized clusters studied here we find that the Homo-Lumo gap and the magnitude of dipole moment of isomeric species can vary drastically.

First principles calculation of the geometric and electronic structure of (Al 2O 3) n(O x) clusters with n

We have studied the geometrical and electronic structure of (Al 2O 3) n (O x ) clusters with n<15 and x=0, 1, 2 by means of first principles density functional calculations, norm-conserving pseudopotentials and a numerical atomic basis set. The equilibrium geometries have been determined by total energy minimization, starting with several initial geometries for each cluster size. The trends obtained for the atomic arrangements (structural isomers, coordination numbers, ‘amorphous’ vs. ‘ordered’ structures, etc.) and the electronic properties (binding energies, HOMO–LUMO gap, density of levels, dipole moments and Mulliken population charges) are discussed. The effect of atomic and molecular oxygen adsorption on these properties is studied.

Time-dependent density functional theory calculations of molecular static and dynamic polarizabilities, cauchy coefficients and their anisotropies with atomic numerical basis functions

Static and dynamic polarizabilities of a range of small first row compounds have been calculated with time-dependent density functional theory in the local spin-density approximation using numerical atomic basis sets. The results are compared to earlier computational work, in particular the work of Van Caillie and Amos [C. Van Caillie, R.D. Amos, Chem. Phys. Lett. 291 (1998) 71], as well as experimental values. The results for static isotropic and anisotropic polarizabilities of H 2O, N 2, CO, NH 3, and CH 4 are in good agreement with previous calculations. The results for the dynamic polarizabilities as expressed in the S(−4) Cauchy coefficients and their anisotropies for H 2O, N 2, CO 2, NH 3, CH 4, C 2H 2, C 2H 4 and C 2H 6 are also in good agreement with previous results. We have also explored the scaling of our implementation of the time-dependent coupled-perturbed Kohn–Sham equations by evaluating the static and dynamic polarizabilities of bifurcated water chains ranging from 1–20 molecules in size.

A molecular cluster approach to the electronic structure of anomalous muonium in diamond

First-principle discrete variational (DV) Xα cluster calculations are used to reproduce muon spin rotation (μSR) experimental data relative to anomalous muonium in diamond. A detailed analysis of the muonium-host interaction is reported. Calculations of the Fermi contact ( A), of the dipolar (2 B) hyperfine (hf) parameters and of the two components of the hf interaction tensor A ( A ∥ and A ⊥) agree well with experimental data only if an optimized numerical atomic basis set is used. Moreover, superhyperfi coupling constants for muonium at the nearest carbon atoms have been also computed. Theoretical data relative to hf quantities indicate that they do not seem to be strongly cluster-size dependent. Finally, the herein reported results have been also compared with other theoretical investigations carried out by using different approaches. The good agreement between our results and the experimental ones, coupled with the quite low computational cost of the DV-Xα approach, are encouraging for further investigations of more complex systems.