$CEEIS group (optional, for extrapolation to FCI limit) The method termed Correlation Energy Extrapolation by Intrinsic Scaling (CEEIS) allows one to extrapolate sequences of CI energies, computed with the ORMAS program, to what is effectively the full CI limit for a given basis set. Typically, the energy for SD and SDT excitation levels using all orbitals (m=M, meaning occupied + all virtuals) is combined, using certain scaling relations, with explicit computations using m orbitals for quadruple, quintuple... excitations (x), using a smaller m for each higher excitation, to obtain the extrapolated FCI limit, within an estimated error bar. When this is done for several basis sets, it is possible to extrapolate the individual full CI energies to the limit of the complete basis set. A series of papers combines complete basis set CEEIS energies with scalar relativistic, spin-orbit, and long range electrostatic corrections to produce a very accurate rotational-vibrational spectrum of F2, see L.Bytautas, T.Nagata, M.S.Gordon, K.Ruedenberg J.Chem.Phys. 127, 164317/1-20 (2007) L.Bytautas, N.Matsunaga, T.Nagata, M.S.Gordon, K.Ruedenberg J.Chem.Phys. 127, 204301/1-12 (2007) L.Bytautas, N.Matsunaga, T.Nagata, M.S.Gordon, K.Ruedenberg J.Chem.Phys. 127, 204313/1-19 (2007) L.Bytautas, K.Ruedenberg J.Chem.Phys. 130, 204101/1-14 (2009) The input description below is quite terse. A full description of how to use CEEIS with ORMAS is provided in a separate file (a Word document) named ~/gamess/tools/ci-tools/ceeis/CEEIS.doc containing a much more detailed description of how to do this kind of calculation. This document explains how to use an Excel spreadsheet to allow visual checking of the energy data that are being extrapolated. Several input examples are given in the same directory. ENREF = reference energy, usually either a zero-excited ORMAS reference wavefunction, or some SCF level energy (if the reference is one determinant). ISTPEX = highest excitation level considered by the CEEIS, the default is 8 (octuple excitations). M1M2EX = an array to specify the various ORMAS computations to be performed, at each excitation level x. 0's start the specification of m values for each level x=3,4,...ISTPEX. Some examples follow, M1M2EX(1)= 0,0,0, 0,7,10,-14,20 0,7,10,-14 ISTEPX=5 The final two zero's on the first (SDT) line mean do the SDT computations with the entire virtual space, and also for all m values used at the higher excitations. The SDTQ energies are found for m=7,10,11,12,13,14,20, that is, the minus sign implies all values in the range 10-14. The SDTQ5 computations do not include m=20. If there is not enough memory to do the entire SDT calculation, this can be extrapolated (losing accuracy in the entire CEEIS process), by input such as M1M2EX(1)= 0,7,10,-14,20,27, 0,7,10,-14,20 0,7,10,-14 ISTEPX=5 Changing the 0,0 part of the triples line to what is shown extrapolates from m=27. Note that it is an error not to include the same m values that higher excitations will use. There is no input for doubles, as in all cases the program will generate the SD energy for the entire virtual space, and additional SD energies for the m values chosen for use by the higher excitation levels. M1M2EX(1)= all 0's will carry out a fully automated CEEIS using MMIN to MMIN+4, testing convergence, possibly adding MMIN+5 to MMIN+9 and so forth. IDELTM = range increment for the m1,m2 ranges given as {m1,-m2} in M1M2EX. Default=1. ISCHME = extrapolation choice (the default is 1) for energy increments (DEMAT = differences of EMAT values): = 1 means extrapolate excitation level "x" by DEMAT(m,x) = a*DEMAT(m,x-2) + b = 2 means extrapolate quadruples as above, but x=5+6 or x=7+8,... are extrapolated together: DEMAT(m,x) = A*DEMAT(m,2) + B*DEMAT(m,3) + C In this case energies for odd excitation levels are not needed, and their computation can be avoided by making the odd levels in M1M2EX be the same input for 5+6, 7+8, ... MMIN = "m" value of the lowest virtual orbital to be considered in the extrapolation. The default is NCORE + 1 + MAX(no. valence e-, no. valence orbs), which is in fact the lowest "m" that should ever be used. XTRTOL = an array of thresholds for each extrapolated energy E(x), if the automated CEEIS is being used. default = 2D-4 Hartree for all levels x. NSEXT = an array containing NSPACE entries. Each entry corresponds to an ORMAS orbital group defined by MSTART in $ORMAS, and can be either 0 or 1. An entry of 1 means include excitations from this space during the CEEIS. 0 means do not include any such excitations, meaning electrons in this subspace are NOT being correlated, apart from the correlation built into the original ORMAS. The final entry in the list is the virtual space, and must be given as 1. The default is all 1's. RESTRT = a flag to say that the CEEIS calculation is being restarted, in which case energies provided in the $CEDATA input are read, and only the missing energies will be calculated. Default = .FALSE. IEXPND = expands the excitation level in restarts, e.g. if the previous data was computed for ISTPEX=6, and you now wish to use ISTPEX=8, enter IEXPND=2 to add two more columns to the matrix EMAT(m,x) being read in $CEDATA. ========================================================== $CEDATA group (optional restart data for CEEIS runs) This group contains previously computed ORMAS energies, forming the EMAT array, to be used to restart CEEIS runs. It is required if RESTRT in $CEEIS is true. ==========================================================

generated on 7/7/2017