1SCF input parameters 2 3Convergence threshold 4 5 THRESH tol 6 7 The convergence criterion is on the maximum value of the gradient 8 vector. The default value is 10^-6. 9 10 11Maximum number of iterations 12 13 MAXITER n 14 15 default is 5 ... usually only 3 are needed. 16 17 e.g. 18 19 maxiter 10 20 21 22Input/output MO vectors 23 24 VECTORS [input] <atomic|hcore|filename> [output <filename>] 25 26 output vectors default to either the same filename as the 27 input vectors if they were read from a file or to the 28 filename movecs (which is searched for by the application). 29 30 E.g. 31 32 These two are equivalent and implement the default 33 34 vectors atomic output movecs 35 36 vectors input atomic output movecs 37 38 This gets input vectors from one file and outputs final 39 vectors back to the same file 40 41 vectors h2o.movecs 42 43 This gets input vectors from one file and outputs final 44 vectors to another file 45 46 vectors input h2o.guess output h2o.final 47 48 49 50SCF level shifting 51 52 LEVEL [pcg initial [tol final]] [nr initial [tol final]] 53 54 Both the 1-electron preconditioned conjgugate gradient (PCG) and 55 the Newton-Raphson (NR) use level shifting to stabilize convergence 56 (by making the preconditioning matices more positive definite and 57 diagonally dominate). For both you can specify an initial level 58 shift, a gradient value at which to change shifts, and a final 59 level shift. The defaults 60 61 pcg initial = 10.0 62 pcg change shift at max. gradient = 0.5 63 pcg final = 0.0 64 nr initial = 10.0 65 nr change shift at max. gradient = 0.5 66 nr final = 0.0 67 68 are almost always acceptable because the program will increase 69 the level shift if convergence problems are encountered with the 70 preconditioning. However, some cases do require increased level 71 shifts to speed convergence 72 73 e.g. 74 75 This enables the default options 76 77 level nr 0 0 0 pcg 10 .5 0 78 79 80Controlling use of newton-raphson quadratically convergent algorithm 81 82 NR tol 83 84 The QC algorithm (use of exact hessian preconditioner) is enabled 85 by default when the maximum element of the orbital gradient falls 86 below 0.1. This value can be changed using this directive 87 88 e.g. 89 90 This enables the default 91 92 NR 0.1 93 94 This disables the QCSCF entirely 95 96 NR 0.0 97 98 99Atomic guess shift (subject to change) 100 101 SET "scf:atom shift" real value 102 103 The atomic guess routines form a density matrix (D) from a superposition 104 of the atomic density matrices. Vectors are obtained from diagonalizing 105 the matrix 106 107 Fock(D) - shift * SDS 108 109 If the density matrix was idempotent then this is equivalent to 110 standard level shifting. The default value of shift is 0.0 which seems 111 best for 'normal' molecules. Values of 1-2 can help with transition metals. 112 There is no special input for this parameter so U have to use the generic 113 set directive. 114 115