Ian P. Grant

Bio: Ian P. Grant is an academic researcher from University of Oxford. The author has contributed to research in topics: Dirac (software) & Electron. The author has an hindex of 39, co-authored 126 publications receiving 9112 citations. Previous affiliations of Ian P. Grant include University of Cambridge & Atlas Computer Laboratory.

Relativistic calculation of atomic structures.

Abstract: The current state of the art in relativistic calculation of atomic structures is surveyed. The theory is modelled on the practice in non-relativistic calculations, using many-particle wave functions built from Dirac central field spinors. The Hamiltonian includes quantum electrodynamic effects in the form of the Breit approximation for the interaction energy of two electrons. Within the limits for which this is valid, it is possible to construct matrices for one- and two-particle operators and hence to perform atomic structure calculations which automatically include the major relativistic effects. The theory can be greatly simplified by using Racah's tensor operators. Major applications have utilized the Hartree or Hartree-Fock methods, and the relevant equations are formulated in detail. Numerical Hartree-Fock solutions for the average of the ground configuration have now been obtained for most elements with atomic number less than 103, and some solutions have also been obtained for ions. The s...

Relativistic quantum theory of atoms and molecules

Abstract: Relativity in atomic and molecular physics.- Relativity in atomic and molecular physics.- Foundations.- Relativistic wave equations for free particles.- The Dirac Equation.- Quantum electrodynamics.- Computational atomic and molecular structure.- Analysis and approximation of Dirac Hamiltonians.- Complex atoms.- Computation of atomic structures.- Computation of atomic properties.- Continuum processes in many-electron atoms.- Molecular structure methods.- Relativistic calculation of molecular properties.- Frequently used formulae and data.- Frequently used formulae and data.- Supplementary mathematics.- Supplementary mathematics.

Light scattering in planetary atmospheres

Abstract: This paper reviews scattering theory required for analysis of light reflected by planetary atmospheres. Section 1 defines the radiative quantities which are observed. Section 2 demonstrates the dependence of single-scattered radiation on the physical properties of the scatterers. Section 3 describes several methods to compute the effects of multiple scattering on the reflected light.

Advances in methods and algorithms in a modern quantum chemistry program package

Abstract: Advances in theory and algorithms for electronic structure calculations must be incorporated into program packages to enable them to become routinely used by the broader chemical community. This work reviews advances made over the past five years or so that constitute the major improvements contained in a new release of the Q-Chem quantum chemistry package, together with illustrative timings and applications. Specific developments discussed include fast methods for density functional theory calculations, linear scaling evaluation of energies, NMR chemical shifts and electric properties, fast auxiliary basis function methods for correlated energies and gradients, equation-of-motion coupled cluster methods for ground and excited states, geminal wavefunctions, embedding methods and techniques for exploring potential energy surfaces.

Electroluminescence from single monolayers of nanocrystals in molecular organic devices

Abstract: The integration of organic and inorganic materials at the nanometre scale into hybrid optoelectronic structures enables active devices that combine the diversity of organic materials with the high-performance electronic and optical properties of inorganic nanocrystals. The optimization of such hybrid devices ultimately depends upon the precise positioning of the functionally distinct materials. Previous studies have already emphasized that this is a challenge, owing to the lack of well-developed nanometre-scale fabrication techniques. Here we demonstrate a hybrid light-emitting diode (LED) that combines the ease of processability of organic materials with the narrow-band, efficient luminescence of colloidal quantum dots (QDs). To isolate the luminescence processes from charge conduction, we fabricate a quantum-dot LED (QD-LED) that contains only a single monolayer of QDs, sandwiched between two organic thin films. This is achieved by a method that uses material phase segregation between the QD aliphatic capping groups and the aromatic organic materials. In our devices, where QDs function exclusively as lumophores, we observe a 25-fold improvement in luminescence efficiency (1.6 cd A(-1) at 2,000 cd m(-2)) over the best previous QD-LED results. The reproducibility and precision of our phase-segregation approach suggests that this technique could be widely applicable to the fabrication of other hybrid organic/inorganic devices.

Systematically convergent basis sets with relativistic pseudopotentials. II. Small-core pseudopotentials and correlation consistent basis sets for the post-d group 16–18 elements

Abstract: A series of correlation consistent basis sets have been developed for the post-d group 16–18 elements in conjunction with small-core relativistic pseudopotentials of the energy-consistent variety. The latter were adjusted to multiconfiguration Dirac–Hartree–Fock data based on the Dirac–Coulomb–Breit Hamiltonian. The outer-core (n−1)spd shells are explicitly treated together with the nsp valence shell with these PPs. The accompanying cc-pVnZ-PP and aug-cc-pVnZ-PP basis sets range in size from DZ to 5Z quality and yield systematic convergence of both Hartree–Fock and correlated total energies. In addition to the calculation of atomic electron affinities and dipole polarizabilities of the rare gas atoms, numerous molecular benchmark calculations (HBr, HI, HAt, Br2, I2, At2, SiSe, SiTe, SiPo, KrH+, XeH+, and RnH+) are also reported at the coupled cluster level of theory. For the purposes of comparison, all-electron calculations using the Douglas–Kroll–Hess Hamiltonian have also been carried out for the haloge...

A generalized split-window algorithm for retrieving land-surface temperature from space

Abstract: Proposes a generalized split-window method for retrieving land-surface temperature (LST) from AVHRR and MODIS data. Accurate radiative transfer simulations show that the coefficients in the split-window algorithm for LST must vary with the viewing angle, if the authors are to achieve a LST accuracy of about 1 K for the whole scan swath range (/spl plusmn/55/spl deg/ from nadir) and for the ranges of surface temperature and atmospheric conditions over land, which are much wider than those over oceans. The authors obtain these coefficients from regression analysis of radiative transfer simulations, and they analyze sensitivity and error over wide ranges of surface temperature and emissivity and atmospheric water vapor abundance and temperature. Simulations show that when atmospheric water vapor increases and viewing angle is larger than 45/spl deg/, it is necessary to optimize the split-window method by separating the ranges of the atmospheric water vapor, lower boundary temperature, and the surface temperature into tractable subranges. The atmospheric lower boundary temperature and (vertical) column water vapor values retrieved from HIRS/2 or MODIS atmospheric sounding channels can be used to determine the range for the optimum coefficients of the split-window method. This new algorithm not only retrieves land-surface temperature more accurately, but is also less sensitive to uncertainty in emissivity and to instrument quantization error.