MacroModel Reference Manual - ISP

Chapter 4: Operation Codes2 H×v is calculated using a LBFGS (see MINI arg1=10) representation of an approximationto the inverse Hessian matrix. This method is the fastest, but it can only beused to calculate the three lowest modes. Higher modes are usually only computationalartifacts: they are totally useless for LLMOD. Check arg4 if you choose thismethod.3 This method is a variant of arg1=1 using spectral transformation to boost convergence.Extremely slow, not recommended. If you choose to try it, check arg6 andarg7.4 Same as arg1=0, but sparse Hessian storage is built on top of an explicit Hessianmatrix. It is faster than arg1=0, but explicit Hessian storage makes it prohibitive formore than approx. 1000 atoms. (The Hessian storage scheme is the same used forTNCG minimization (MINI arg1=9).5 H×v is calculated with exact arithmetic. The Hessian is not stored in any form, itselements are always recalculated as they are needed for computing v k (i)=H(i,j)*v l (j)and v k (j)=H(i,j)*v l (i). This is the most accurate method, but it is prohibitively slowon large molecules because of the burden of recalculating the Hessian numeroustimes.arg2Dimension of “small” problems to solve (length of Arnoldi factorization)0 Default: 300>0 Other value to be used. arg2 >= requested number of modes + 1 (LMC2 arg3, VBR2arg2), recommended value: arg2 = 10 * requested number of modesarg3Number of “small” problems to solve (number of Arnoldi iterations)0 Default: 450>0 Other value to be used (maximum 25,000).arg4This argument is multipurpose.If arg1=2, then arg4 specifies the number of extra LBFGS steps applied after minimizationhas reached convergence, to build a more accurate LBFGS representationof the Hessian matrix.0 Default: 500>0 Other value to be used.MacroModel 9.7 Reference Manual 99