- 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).

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molpro@molpro.net 2018-04-19