CASTEP

CASTEP Molecular Simulations Inc., 9685 Scranton Road, San Diego, California, USA. 

The pseudopotential density-functional technique is used to calculate total energies, forces on atoms and stress tensors as described in Ref. 13 and implemented in the computer code CASTEP. CASTEP uses a plane-wave basis set to expand wave-functions and a preconditioned conjugate gradient scheme to solve the density-functional theory (DFT) equations iteratively. Brillouin zone integration is carried out via the special points scheme by Monkhorst and Pack. The nonlocal pseudopotentials in Kleynman-Bylander form were optimized in order to achieve the best convergence with respect to the basis set size. 5... 

CASTEP is a DFT program code distributed inside the Materials Studio package version 2.2.1 2002 Accerys Inc., San Diego-... 

Density functional theory has been extensively used to calculate vibrational properties of minerals and other crystalline phases in addition to molecules and molecule-like substances. This method has recently begun to be used to calculate isotope fractionation factors (Schauble et al. in press Anbar et al. in press), and shows great potential for future research. Programs such as ABINIT (Gonze et al. 2002), pwSCF (Baroni et al. 2001)—both freely available—and the commercial package CASTEP (Accelrys, Inc.) can be used to calculate vibrational properties of crystals. 

The electric-structure-calculation presented here is performed using the CASTEP computer code, which is based on density functional theory, aided by the CERIUS2 graphical front-end. The wave functions are expended in a plane wave basis set, and the effective potential of ions is described by ultrasoft pseudo potential. 

The proper way of dealing with periodic systems, like crystals, is to periodicize the orbital representation of the system. Thanks to a periodic exponential prefactor, an atomic orbital becomes a periodic multicenter entity and the Roothaan equations for the molecular orbital procedure are solved over this periodic basis. Apart from an exponential rise in mathematical complexity and in computing times, the conceptual basis of the method is not difficult to grasp [43]. Software for performing such calculations is quite easily available to academic scientists (see, e.g., CASTEP at www.castep.org CRYSTAL at www.crystal.unito.it WIEN2k at www.wien2k.at). 

Experimental data supported by first-principles calculations. Static data collected at 14.1 T at 292 and 150 K, which showed significant deviation from the CASTEP calculations attributed to the limitations of the pseudopotentials used. 

Cerius2 Users Guide and Materials Studio 2.1.5 Users Guide for CASTEP, MSI and Accelrys Inc., 2000-2002. 

The main purpose of quantum-chemical modeling in materials simulation is to obtain necessary input data for the subsequent calculations of thermodynamic and kinetic parameters required for the next steps of multiscale techniques. Quantum-chemical calculations can also be used to predict various physical and chemical properties of the material in hand (the growing film in our case). Under quantum-chemical, we mean here both molecular and solid-state techniques, which are now implemented in numerous computer codes (such as Gaussian [25], GAMESS [26], or NWCHEM [27] for molecular applications and VASP [28], CASTEP [29], or ABINIT [30] for solid-state applications). 

Fig. 3. Top (A) and side (B) views of the DFT structure of the p(4 x 4)-Aglg30/ Ag lll. Numbers 1-9 are given to representative Ag atoms, which are represented by light grey balls in the oxide overlayer and light grey sticks in the 111 substrate. Dark grey balls with u and d labels describe up and down oxygen atoms forming the O bilayer. The table on the right gives key structural parameters obtained with VASP and CASTEP.

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