First-principles electronic structure

Luce T A and Bennemann K H 1998 Nonlinear optical response of noble metals determined from first-principles electronic structures and wave functions calculation of transition matrix elements P/rys. Rev. B 58 15 821-6... 

Our work demonstrates that EELS and in particular the combination of this technique with first principles electronic structure calculations are very powerful methods to study the bonding character in intermetallic alloys and study the alloying effects of ternary elements on the electronic structure. Our success in modelling spectra indicates the validity of our methodology of calculating spectra using the local density approximation and the single particle approach. 

Millam, J. M., Scuseria, G. E., 1997, Linear Scaling Conjugate Gradient Density Matrix Search as an Alternative to Diagonalization for First Principles Electronic Structure Calculations , J. Chem. Phys., 106, 5569. 

The structure and dynamics of clean metal surfaces are also of importance for understanding surface reactivity. For example, it is widely held that reactions at steps and defects play major roles in catalytic activity. Unfortunately a lack of periodicity in these configurations makes calculations of energetics and structure difficult. When there are many possible structures, or if one is interested in dynamics, first-principle electronic structure calculations are often too time consuming to be practical. The embedded-atom method (EAM) discussed above has made realistic empirical calculations possible, and so estimates of surface structures can now be routinely made. 

In contrast to the discussion above with amorphous barriers, it is possible to use first-principles electron-structure calculations to describe TMR with crystalline tunnel barriers. In the Julliere model the TMR is dependent only on the polarization of the electrodes, and not on the properties of the barrier. In contrast, theoretical work by Butler and coworkers showed that the transmission probability for the tunneling electrons depends on the symmetry of the barrier, which has a dramatic influence on the calculated TMR values [20]. In the case of Fe(100)/Mg0(100)/Fe (100) the majority of electrons in the Fe are spin-up. They are derived from a band of delta-symmetry. In 2004 these theoretical predictions were experimentally confirmed by Parkin et al. and Yusha et al. [21, 22]. Remarkably, by 2005 TMR read heads were introduced into commercial hard disk drives. 

It has been empirically known that the energies of the lowest excited state of tetrahedrally coordinated metals decrease in the order Cr + < Mn + < Fe ". As in the case of 3cf elements, this tendency has been considered to originate from the difference in covalency, which reduced two-electron repulsion between the electrons occupying 3d orbitals. Recently this question was treated using first-principles electronic-structure calculation (Ishii et al. 2002). The same tendencies were found as for the 3d ions. Distance dependent multiplet-energy diagrams for these elements have been obtained (Fig. 5.34), which enable us to envisage the typical shapes of the possible emissions. As in... 

Electronic Structure Calculations. We have used first-principles electronic structure calculations as manifest in the (spin) density functional linearized muffin-tin orbital method to examine whether the asymmetry in properties is reflected in a corresponding asymmetry in the one-electron band structure. While in a more complete analysis explicit electron correlation of the Hubbard U type would be intrinsic to the calculation,17 we have taken the view that one-electron bandwidths point to the possible role that correlation might play and that correlation could be a consequence of the one-electron band structure rather than an integral part of the electronic structure. We have chosen the Lai- Ca,Mn03 system for our calculations to avoid complications due to 4f electrons in the corresponding Pr system. 

In addition to the development in the methodology to compute electronic structures, there have been several attempts to handle the simulation of a chemical event in a system with a large number of degrees of freedom. The Car-Parrinello (CP) approach [5], often referred to as first-principles molecular dynamics (FPMD) method, opened the way to the molecular dynamics simulations based on the first-principles electronic structure calculations. The point of the method is to circumvent the explicit... 

Equation (2) is an example of a sum-over-states (SOS) expression of a molecular response property. It suggests an easy way of computing / , but in practice the SOS approach is rarely taken because of its very slow convergence, i.e., because of the need to compute many excited states wavefunctions. The summation goes over all excited states and also needs to include, in principle, the continuum of unbound states. As it will be shown below, there are more economic ways of computing [1 within approximate first-principles electronic structure methods. 

As discussed below in detail, first-principles electronic structure calculations have provided accurate predictions of the reaction pathways and the corresponding energy barriers, not only for the first step of hydrolysis of cocaine free base at the benzoyl ester group, but also for the entire reaction processes of hydrolysis of cocaine free base at both the benzoyl ester and methyl ester groups. 

Wang, C. S., and B. M. Klein (1981). First-principles electronic structure of Si, Ge, Gap GaAs, ZnS, and ZnSe. I. Self-consistent energy bands, charge densities, and effective masses. Phys. Rev. B24, 3393-416. 

S. Sapra, D. D. Sarma, Proceedings of the 3rd Japan-Korea Joint Workshop on First-Principles Electronic Structure Calculations Oct.-Nov. 2001, p. 105. 

Zhan, C.G., Dixon, D.A. Absolute hydration free energy of the proton from first-principles electronic structure calculations. J. Phys. Chem. A 2001,105(51), 11534M0. 

Huge systems like DNA are not accessible by traditional first-principles algorithms as employed in electronic structure theory. However, first-principles electronic structure methods are often needed in order to achieve the necessary level of accuracy for either benchmark calculations that may serve as a reference or in cases where a detailed molecular picture is mandatory. It is therefore desirable to further develop ab initio and DFT methods in the context of multiscale modeling [147]. Examples for extended first-principles CPMD calculations on electronic and optical properties of DNA and on the reactivity of radical cations can be found in Refs. [148-150]. 

In the first part of this work, a brief overview over several strategies to combine such time domain transport simulations with first principles electronic structure theory is given. For the latter, we restrict ourselves to a discussion of time dependent density functional theory (TDDFT) only. This method is by far the most employed many body approach in this field and provides an excellent ratio of accuracy over computational cost, allowing for the treatment of realistic molecular devices. This digest builds on the earlier excellent survey by Koentopp and co-workers on a similar topic [13]. Admittedly and inevitably, the choice of the covered material is biased by the authors interests and background. 

Wang C S and Klein B M 1981 First-principles electronic structure of Si, Ge, GaP, GaAs, ZnS and ZnSe. II. Optical properties Phys. Rev. B 24 3417-29... 

---