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Manuscript Title: Force calculation and atomic-structure optimization for the full- potential linearized augmented plane-wave code WIEN.
Authors: B. Kohler, S. Wilke, M. Scheffler, R. Kouba, C. Ambrosch-Draxl
Program title: fhi95force
Catalogue identifier: ADCW_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 94(1996)31
Programming language: Fortran.
Computer: IBM RS/6000.
Operating system: AIX, UNICOS.
RAM: 64M words
Word size: 64
Keywords: Density functional Theory, Linearized augmented Plane wave method, Lapw, Supercell, Total energy, Structure optimization, Molecular dynamics, Crystal field, Structure, Molecules, Forces, Solid state physics.
Classification: 7.3, 16.1.

Subprograms used:
Cat Id Title Reference
ABRE_v1_0 WIEN CPC 59(1990)399

Nature of problem:
For ab-initio studies of the electronic and magnetic properties of poly- atomic systems, such as molecules, crystals and surfaces, it is of paramount importance to determine stable and metastable atomic geometries. This task of structure optimization is greatly accelerated and, in fact, often only feasible if the forces acting on the atoms are known. The computer code described in this article enables such calculations.

Solution method:
The full-potential linearized augmented plane wave (FP-LAPW) method is well known to enable accurate calculations of the electronic structure and magnetic properties of crystals [1, 2, 3, 4, 5, 6, 7, 8]. Within the supercell approach it has also been used for studies of defects in the bulk and for crystal surfaces. For the evaluation of the atomic forces within this method we follow the approach outlined by Yu and coworkers [9]. In order to minimize the total energy as a function of atomic positions we employ a damped Newton dynamics scheme [10] or alternatively the variable metric algorithm of Broyden et al [11, 12, 13]. Several applications of this approach to chemisorption at surfaces have already been published [14, 15].

Restrictions:
Inversion and orthorombic symmetry of the elementary cell is required.

Running time:
The additional force calculation increases the running time of a typical self-consistent total energy calculation by 5-10%.

References:
[1] D.D. Koelling, J. Phys. Chem. Solids 33 (1972) 1335; D.D. Koelling and G.O. Arbman, J. Phys. F 5 (1975) 2041.
[2] O.K. Andersen, Solid State Commun. 13 (1973) 133; Phys. Rev. B 12 (1975) 3060.
[3] E. Wimmer, H. Krakauer, M. Weinert and A.J. Freeman, Phys. Rev. B 24 (1981) 864.
[4] H.J.F. Jansen and A.J. Freeman, Phys. Rev. B 33 (1986) 561.
[5] L.F. Mattheiss and D.R. Hamann, Phys. Rev. B 33 (1986) 823.
[6] P. Blaha, K. Schwarz, P. Sorantin and S.B. Trickey, Comput. Phys. Commun. 59 (1990) 399.
[7] P. Blaha, K. Schwarz and R. Augustyn, WIEN93 (Technical University, Vienna, 1993); improved and updated UNIX version of the original copy-righted WIEN-code
[6] .
[8] D.J. Singh, Planewaves, pseudopotentials and the LAPW method (Kluwer Academic, Boston, 1994).
[9] R. Yu, D. Singh and H. Krakauer, Phys. Rev. B 43 (1991) 6411.
[10] R. Stumpf and M. Scheffler, Comp. Phys. Commun. 79 (1994) 447.
[11] C.G. Broyden, J.E. Dennis and J.J. More, J. Inst. Maths. Appl. 12, 223 (1973).
[12] K.W. Brodlie, in The State of the Art in Numerical Analysis, ed. D.A.H. Jacobs (Academic Press, London, 1977).
[13] J.E. Dennis and R.B. Schnabel, Numerical Methods for Unconstrained Optimization and Nonlinear Equations (Prentice-Hall, Englewoods Cliffs, 1983).
[14] B. Kohler, P. Ruggerone, S. Wilke and M. Scheffler, Phys. Rev. Lett. 74 (1995) 1387.
[15] S. Wilke and M. Scheffler, Surf. Sci. 329 (1995) L605.