Execution of LMTO

The execution of LMTO requires a data set with the appropriate structure constant matrices, and, if requested, a data set containing correction-term structure constant matrices. These matrices must be generated in previous runs of STR and COR and stored in STR/XXX/A and COR/XXX/B, respectively. 

They form the bulk of the input data for LMTO. The additional input needed is essentially the appropriate potential parameters, exemplified in Table 9.4. 

The second line of the input contains 80 characters of text describing the potential parameters to follow. It is often useful to include here the date at which these parameters were generated. The text will be included in the energy-band file BND/YY/B and printed by programmes which access this file. 

The third line contains the atomic Wigner-Seitz radius S. in atomic units for the atom of type t here labelled by the type number IT(IQ). Instead of the actual radius one may give an arbitrary number SWP(I), which will be used by the subroutine SCASW to generate the radius (radii) according to (9.10). TTXT(IQ) is the usual chemical symbol for the atom with type number IT(IQ). 

The next NL lines contain and the four standard potential parameters defined by (4.1). To be able to specify J2 = 0 the fourth parameter must be given as j 2. If the primitive cell holds more than one atom, each extra atom should be.described by data analogous to the above NL + 2 lines. 

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In summary, the self-consistency procedure has two iteration loops. One is based upon the enerqy-soaKng principle of Sect.2.6 and implemented in SCFC, and the other is based upon band calculations and therefore requires consecutive execution of LMTO, DDNS and SCFC. At the end of the scaling iterations, and hence also at the end of a band iteration, one may compare the calculated ground-state properties with previous band iterations. If convergence is obtained one may stop at this point. If not, one may start a new band iteration using the potential parameters from the last scaling iteration. 

The file BND/YY/B, which after execution of LMTO (if NOEVC = 1) contains the eigenvalues and ti characters, is a random (direct) access file. This file organisation very often causes problems when LMTOPACK is implemented on machines other than Burroughs B7800. The problem is that the Burroughs, for which the programmes were written, allows sequential write and subsequent random read in a file with fixed record length, while most other machines do not. 

Hence, we have in effect two iteration loops, a band loop consisting of a consecutive execution of LMTO, DDNS, and SCFC, and a scaling loop formed by the scaling procedure inside SCFC, see Fig.9.1. For many applications the latter will suffice. 

Upon completion, the programme will print the four standard potential parameters per z9 some other potential parameters, e.g. masses and band edges, zeroth-, first-, and second-order moments of the state density, and partial and total pressures. If the potential parameters in the original run of LMTO have been suitably chosen, one will have a reasonably converged result after just one execution of SCFC. If this is not the case, one must use the output potential parameters to perform new band-structure and state-density calculations, and then repeat SCFC with the new state densities. 

The STR may be used to calculate the canonical structure constants defined by (6.7-9) or (8.23,24). In a typical application the programme is executed once for a given crystal structure. It produces and stores on disk or tape a set of structure-constant matrices distributed on a suitable grid in the irreducible wedge of the Brillouin zone. Whenever that particular crystal structure is encountered, the structure constant matrices may be retrieved and used to set up the LMTO eigenvalue problem which, in turn, leads to the energy bands of the material considered. 

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