UT theoretical chemistry code forum

Dear all,

I want to know that how the reaction coordinate of a particular image is being calculated in NEB. It should depend up on atomic positions, but how it determine reaction coordinates from that?
Another question is what should be ideal distance between the images for good convergence. Some times I find that my images are 2-2.5 A apart and calculation is having convergence problem whereas angles between the images were greater than 90 degree.

Thanks in advance.

The reaction coordinate could be defined as the set of coordinates along the minimum energy path (MEP). Based upon that definition, it doesn't make sense to talk about the reaction coordinate at an image. The tangent, perhaps, which is defined in the NEB as the vector to the higher energy neighboring image.

The second question, about the appropriate resolution along the MEP is strongly dependent upon the complexity of the pathway. A linear path would require a single climbing image. If you are finding that the image are spaced by a large distance and/or small angles between images, I suggest looking for any intermediate minima along the path so that you can break up your calculation into individual calculations for the separate elementary steps.