Optical properties of clusters and molecules from real-time time-dependent density functional theory using a self-consistent field

We present a detailed study of optical absorption spectra of finite-size structures, using a method based on time-dependent density-functional theory (TDDFT), which involves a self-consistent field for the propagation of the Kohn–Sham wavefunctions in real-time. Although our approach does not provide a straightforward assignment of absorption features to corresponding transitions between Kohn–Sham orbitals, as is the case in frequency-domain TDDFT methods, it allows the use of larger timesteps while conserving total energy and maintaining stable dipole moment oscillations. These features enable us to study larger systems more efficiently. We demonstrate the efficiency of our method by applying it to a hydrogen-terminated silicon cluster consisting of 364 atoms, with and without P impurities. For cases where direct comparison to experiment can be made, we reproduce the absorption features of fifteen small molecules [N₂, O₂, O₃, NO₂, N₂O, NH₃, H₂O, H₂CO, H₂CO₃, CO₂, CH₄, C₂H₂, C₂H₄, C₂H₆, C₆H₆] and find generally good agreement with experimental measurements. Our results are useful for the detection and the determination of orientation of these molecules.     

Memory in time-dependent density functional theory

Exact time-dependent density functionals remember both the entire history of the density and the initial wave function. We show that the two effects are intimately related, and all history dependence can be written as initial-state dependence, including that of the exchange-correlation kernel. For states that can be evolved from a ground state, all initial-state dependence is a dependence on a pseudo-prehistory, providing a route to excited-state densities from time-dependent density functional theory.     

Stability of small Ni-Ti bimetallic clusters studied by density functional theory

The low-energy structures and the electronic and themagnetic properties of small NiNiNi$_{m}$Ti$_{n}$ clusters, lowest-energy structure,electronic and magnetic propertiesProject supported by the NationalNatural Science Foundation of China (Grant No.~10874039), and theNatural Science Foundation of Hebei Province of China (GrantNos.~A2009000246 and 2009000243).3120A, 3640B, 2110K7/3/2009 12:00:00 AMThe low-energy structures and the electronic and themagnetic properties of small NiNiNi$_{m}$Ti$_{n}$ clusters, lowest-energy structure,electronic and magnetic propertiesProject supported by the NationalNatural Science Foundation of China (Grant No.~10874039), and theNatural Science Foundation of Hebei Province of China (GrantNos.~A2009000246 and 2009000243).3120A, 3640B, 2110K7/3/2009 12:00:00 AMThe low-energy structures and the electronic and themagnetic properties of small Ni$_{n}$Ti$_{n}$ ($n=1$--$6$) andNi$_{m}$Ti$_{n}$ ($1 le n le 4$, $1 le m le 4$, $n ne m$)clusters are investigated by performing all-electron calculationsbased on density functional theory. Ground states and severalisomers near the ground states are determined for these clusters.The results indicate that the growth of small Ni$_{m}$Ti$_{n}$clusters prefers to form rich Ti--Ni and Ti--Ti bonds. When thepercentage of titanium atoms is significantly greater than that ofnickel atoms, the nickel atoms are most frequently found abovethe surface; in contrast, the titanium atoms prefer the bridgingsites. A M\"{u}lliken spin population analysis indicates that thetotal spin of titanium-nickel clusters is not always zero.http://cpb.iphy.ac.cn/CN/10.1088/1674-1056/19/4/043102https://cpb.iphy.ac.cn/CN/article/downloadArticleFile.do?attachType=PDF&id=111644NimTin;clusters;lowest-energy;structure;electronic;and;magnetic;propertiesThe low-energy structures and the electronic and the magnetic properties of small Nin Tin(n = 1-6) and Ni m Ti n(1 ≤ n ≤ 4,1 ≤ m ≤ 4,n ≠ m) clusters are investigated by performing all-electron calculations based on density functional theory.Ground states and several isomers near the ground states are determined for these clusters.The results indicate that the growth of small Ni m Ti n clusters prefers to form rich Ti-Ni and Ti-Ti bonds.When the percentage of titanium atoms is significantly greater than that of nickel atoms,the nickel atoms are most frequently found above the surface;in contrast,the titanium atoms prefer the bridging sites.A Mu¨lliken spin population analysis indicates that the total spin of titanium-nickel clusters is not always zero.     

Nonadiabatic ab initio molecular dynamics using linear-response time-dependent density functional theory

We review our recent work on ab initio nonadiabatic molecular dynamics, based on linear-response timedependent density functional theory for the calculation of the nuclear forces, potential energy surfaces, and nonadiabatic couplings. Furthermore, we describe how nuclear quantum dynamics beyond the Born-Oppenheimer approximation can be performed using quantum trajectories. Finally, the coupling and control of an external electromagnetic field with mixed quantum/classical trajectory surface hopping is discussed.     

Excited states dynamics in time-dependent density functional theory

We present numerical simulations of femtosecond laser induced dynamics of some selected simple molecules -- hydrogen, singly ionized sodium dimer, singly ionized helium trimer and lithium cyanide. The simulations were performed within a real-space, real-time, implementation of time-dependent density functional theory (TDDFT). High harmonic generation, Coulomb explosion and laser induced photo-dissociation are observed. The scheme also describes non-adiabatic effects, such as the appearance of even harmonics for homopolar but isotopically asymmetric dimers, even if the ions are treated classically. This TDDFT-based method is reliable, scalable, and extensible to other phenomena such as photoisomerization, molecular transport and chemical reactivity.Received: 15 October 2003PACS: 33.80.Gj Diffuse spectra; predissociation, photodissociation - 33.80.Wz Other multiphoton processes     

Spin dynamics from time-dependent density functional perturbation theory

We present a new method to model spin-wave excitations in magnetic solids, based on the Liouville–Lanczos approach to time-dependent density functional perturbation theory. This method avoids computationally expensive sums over empty states and naturally deals with the coupling between spin and charge fluctuations, without ever explicitly computing charge-density susceptibilities. Spin-wave excitations are obtained with one Lanczos chain per magnon wave-number and polarization, avoiding the solution of the linear-response problem for every individual value of frequency, as other state-of-the-art approaches do. Our method is validated by computing magnon dispersions in bulk Fe and Ni, resulting in agreement with previous theoretical studies in both cases, and with experiment in the case of Fe. The disagreement in the case of Ni is also comparable with that of previous computations.     

Photoemission spectra of deuterated silicon clusters: experiment and theory

We compare experimentally measured and ab initio computed photoelectron spectra of negatively charged deuterated silicon clusters ( , 4m10, 0n2) produced in a plasma environment. Based on this comparison, we discuss the kinetics and thermodynamics of the cluster formation and the effect of deuterium on the geometrical and electronic structure of the clusters.     

基于密度泛函理论的三聚氰胺结构及振动光谱研究

利用密度泛函(DFT)算法,对三聚氰胺分子的空间结构进行了优化;然后分别用MP2/6-31G和DFT/DGTIVP两种算法计算了它的拉曼光谱与红外光谱,给出光谱强度图;对比了两种算法的拉曼光谱图和其实验光谱图,结果显示了很好的一致性;给出了三聚氰胺分子中的各原子间键长,键角等空间结构参数;并对三聚氰胺分子在550～3 800cm-1区间的振动谱做了指认。上述工作将有助于食品中三聚氰胺含量测量技术的研究。     

Computational studies of CO and CO: Density functional theory and time-dependent density functional theory

Potential energy curves, equilibrium interatomic distances, term energies and harmonic vibration frequencies for the 16 lowest states of neutral carbon monoxide and the six lowest states of singly ionized carbon monoxide are calculated by density functional theory (DFT) and linear-response time-dependent density functional (LR-TDDFT) theory. The results are compared with experimental data. The two theories, DFT and LR-TDDFT, are described briefly.     

Geometries, stabilities and electronic properties of small Nb-doped gallium clusters: A density functional theory study

The host Ga_n+1 and doped Ga_nNb (n=1-9) clusters with several spin configurations have been systematically investigated by a relativistic density functional theory (DFT) with the generalized gradient approximation. The optimized equilibrium geometries tend to prefer the close-packed configurations for small Nb-doped gallium clusters up to n=9. The average binding energies per atom (E_b/atom), second-order differences of total energies (Δ₂E), fragmentation energies (E_f) and HOMO-LUMO gaps of Ga_n+1 and Ga_nNb (n=1-9) clusters are studied. The results indicate the doping of Nb atom in gallium clusters improves the chemical activities. In particular, the clusters with sizes of Ga₄Nb and Ga₇Nb are found to be more stable with respect to their respective neighbors. Our calculated vertical ionization potentials (VIPs) exhibit an obvious oscillating behavior with the cluster size increasing, except for Ga₃ and Ga₄Nb, suggesting the Ga₃, Ga₅, Ga₇, GaNb, Ga₃Nb, Ga₆Nb and Ga₈Nb clusters corresponding to the high VIPs. In the case of vertical electron affinities (VEAs) and chemical hardness η, VEAs are slightly increasing whereas chemical hardness η decreasing as Ga_nNb cluster size increases. Besides, the doping of Nb atom also brings the decrease as the cluster sizes increases for atomic spin magnetic moments (μ_b).     

A density functional theory study on the H2S molecule adsorption onto small gold clusters

An all-electron scalar relativistic calculation on Au_nH₂S (n = 1-13) clusters has been performed by using density functional theory with the generalized gradient approximation at PW91 level. The small gold cluster would like to bond with sulfur in the same plane and the H₂S molecule prefers to occupy the on-top and single fold coordination site in the cluster. The Au_n structures and H₂S molecule in all Au_nH₂S clusters are only slightly perturbed and still maintain their structural integrity. After adsorption, the S-H, H-H bond-lengths and most Au-Au bond-lengths are elongated, only a few Au-Au bond-lengths far from H₂S molecule are shortened. The reactivity enhancement of H₂S molecule is obvious and the strong gold-sulfur bond is observed expectedly. The most favorable adsorption takes place in the case that the H₂S molecule is adsorbed by an even-numbered Au_n cluster and becomes Au_nH₂S cluster with even number of valence electrons. It is believed that the strong scalar relativistic effect is favorable to H₂S molecule adsorption onto small gold clusters and is also one of the important reasons for the strong gold-sulfur bond.     

First-principles simulations for attosecond photoelectron spectroscopy based on time-dependent density functional theory

We develop a first-principles simulation method for attosecond time-resolved photoelectron spectroscopy. This method enables us to directly simulate the whole experimental processes, including excitation, emission and detection on equal footing. To examine the performance of the method, we use it to compute the reconstruction of attosecond beating by interference of two-photon transitions (RABBITT) experiments of gas-phase Argon. The computed RABBITT photoionization delay is in very good agreement with recent experimental results from [Klünder et al., Phys. Rev. Lett. 106, 143002 (2011)] and [Guénot et al., Phys. Rev. A 85, 053424 (2012)]. This indicates the significance of a fully-consistent theoretical treatment of the whole measurement process to properly describe experimental observables in attosecond photoelectron spectroscopy. The present framework opens the path to unravel the microscopic processes underlying RABBITT spectra in more complex materials and nanostructures.     

Nonlocal density functional theory of solids: Applications of the weighted density approximation to silicon

Using the density functional formalism together with the weighted density approximation (WDA), we have carried out selfconsistent bandstructure studies of bulk Si in order to identify the influences of different WDA potentials and different pair correlation functions on the electronic spectrum. Improvements of band energies due to consideration of nonlocalities in exchange and correlation energy depend very sensitively on the particular correlation function used. For the prototype semiconductor Si, only one of the six WDA versions tested seems useful.     

Infrared-transmission spectra and hydrogen content of hydrogenated amorphous silicon

The hydrogenated amorphous silicon (a-Si:H) thin film has excellent optical char-acteristics, such as broad optical energy gap (about 1.67 eV), high photosensitivity (the ratio of photoconductivity to dark conductivity s p/s d is about 105—106 in order) andcheapness. It is a suitable material for the solar energy cell. Because the hydrogen con-tent and silicon-hydrogen bonding configurations in a-Si:H significantly affect its optical and electrical characteristics[1,2], the determination of…     

Vibrational analysis of L-serine using the density functional theory

In this paper, we present a computational study of L-serine using ab initio molecular dynamics simulation based on density functional theory (DFT) within the ultrasoft pseudopotentials and generalized-gradient approximation. Taking into account the intermolecular interactions, we can indeed simulate the features of the experimental results very well for L-serine zwitterions in its solid state. The vibrational spectrum of L-serine performed by DFT was in excellent agreement with our previous inelastic incoherent neutron scattering spectra measured at 20K for L-serine in the 10--200meV region on HET spectrometers at ISIS, Rutherford Appleton Laboratory.     

糠醛分子表面增强拉曼光谱的密度泛函理论研究

采用密度泛函理论(density functional theory,DFT),在B3LYP/6-31+G**(C,H,O)/LANL2DZ(Ag)水平上,对糠醛(furfural,FUR)分子进行了几何结构优化,并计算了FUR分子的常规拉曼散射(normal Raman scattering,NRS)光谱和FUR与Ag原子以及Ag2和Ag4团簇吸附的表面增强拉曼散射(surface-enhanced Raman scattering,SERS)光谱。结果表明,理论值与已有的实验值符合得较好,采用FUR-Ag4吸附构型的计算结果比FUR-Ag和FUR-Ag2吸附构型的计算结果更符合已有实验值。最后,通过Gauss View可视化软件,对FUR分子的振动频率进行了更为全面地归属。通过FUR分子SERS与NRS的比较,可得出FUR分子与Ag原子发生了相互作用,且被吸附的糠醛分子的杂五环是与银表面垂直的。     

对巯基苯胺分子表面增强拉曼光谱的密度泛函理论研究

采用密度泛函理论(density functional theory,DFT),在B3LYP/6-31++-G** (C,H,N,S)/LANL2DZ(Ag)水平上,对对巯基苯胺(p-aminothiophenol,PATP)分子进行了几何结构优化,计算了 PATP的常规拉曼散射(normal Raman scatte...