- J. Nocedal. “Updating quasi-Newton matrices with limited storage”. Math. Comput. 35, 773 (1980).
- D. C. Liu and J. Nocedal. “On the limited memory BFGS method for large scale optimization”. Math. Program. 45, 503 (1989).

The geometry of the well minimum should be specified with the `geometry` keyword.
The action of the instanton, its fluctuations and the fluctuations about the well minimum are printed to the output file.
MOLPRO computes the tunnelling-matrix element which can be used to construct the tunnelling-splitting pattern for a molecular cluster with two or more degenerate wells as described in the latter of the two references.
It is necessary to converge the results in the limit that
and
.

References for the ring-polymer instanton method are:

- J. O. Richardson and S. C. Althorpe. “Ring-polymer instanton method for calculating tunneling splittings.” J. Chem. Phys. 134, 054109 (2011).
- J. O. Richardson, S. C. Althorpe and D. J. Wales. “Instanton calculations of tunneling splittings for water dimer and trimer.” J. Chem. Phys. 135, 124109 (2011).

molpro@molpro.net 2019-01-15