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README
This example shows how to use both pw.x and cp.x to calculate the minimum energy path (MEP) of a simple activated reaction i.e. the collinear proton transfer reaction : H2 + H <==> H + H2 The MEP is obtained by means of the Climbing-Image Nudged Elastic Band (CI-NEB) method and two different climbing image algorithms are used ("auto" and "manual"). (for the meaning of the cited input variables see the appropriate INPUT_* file) The symmetric reaction path H2 + H <==> H + H2 is calculated in three different ways. First using pw.x: 1) The path connecting the initial and the final configurations is discretized with an odd number of images (7) so that the standard CI_scheme ("auto") will give rise to a symmetric MEP (3 images on the left of the saddle point and 3 images on the right). Note that in this system the use of the climbing image is not neccesary. Indeed using CI_scheme = "no-CI" the result is the same. 2) The path connecting the initial and the final configurations is discretized with an even number of images (8) and no climbing image is used. The resulting path is symmetric, but no image is at the saddle point. 3) The path connecting the initial and the final configurations is again discretized with an even number of images (8), but the "manual" CI_scheme is used so that the resulting path is asymmetric. The image 5 now is at the saddle point. Then using cp.x 4) Same as for the first calculation, but with a Car-Parrinello approach. Given the low accuracy of these calculations (plane waves cut-off and thresholds) and the small box employed, these results can not be compared with experiments or with other "ab initio" calculations.