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Using internal coordinates in GAMESS is a real pain. … You should look into the GAMESS manual for more detailed explanations. …

You are using Cartesian coordinates for optimization, and GAMESS by default will attempt to eliminate the rotational and translational modes from the guess hessian, before the optimization starts. … If the algorithm cannot find 5 or 6 modes which match its criteria, then it throws this error and GAMESS stops. There are two ways to solve this: You can use internal coordinates to optimize. …

This is the first part of the output of an RHF/MIDI calculation on an $\ce{H2O}$ molecule with GAMESS(US): ------------ EIGENVECTORS ------------ 1 …

But the problem is that the program I am using (GAMESS) requires the charge and multiplicity of each of the fragments to be defined. I have done EDA before with neutral systems. …

I am new to computational chemistry, I have used mainly GAMESS and Orca. … There is also the NBO program which can interface with GAMESS. It produces 'natural bonding orbitals' which are also said to resemble the traditional bonding types in organic chemistry. …

Short answer: I suspect there is a bug in GAMESS Long answer: First of all I would advise you to go through the manual of GAMESS. … Finally, GAMESS cannot run numerical optimizations and numerical hessians in the same run (i.e. you cannot use HSSEND=.t. with NUMGRD=.t.). …

The manuals of the common softwares (Gaussian, GAMESS, orca etc.) don't mention clearly if they have any such method. … For example, GAMESS manual mentions an 'integral screening' but that seems to refer to ignoring 2e-integrals that contribute very little to the energy. …

However, this method seems to be well-established, because even old versions of GAMESS-US have an option of GUESS=RDMINI in the $GUESS section, which seems to be doing the same thing—reading the converged …