diff --git a/doc/src/fix_neb.rst b/doc/src/fix_neb.rst index ccd0f9b83d..51066675b8 100644 --- a/doc/src/fix_neb.rst +++ b/doc/src/fix_neb.rst @@ -109,7 +109,7 @@ Note that in this case the specified *Kspring* is in force/distance units. With a value of *ideal*, the spring force is computed as suggested in -ref`(WeinanE) ` +:ref:`(WeinanE) ` .. math:: @@ -120,18 +120,18 @@ and :math:`RD_{ideal}` is the ideal *RD* for which all the images are equally spaced. I.e. :math:`RD_{ideal} = (i-1) \cdot meanDist` when the climbing replica is off, where *i* is the replica number). The *meanDist* is the average distance between replicas. Note that in this -case the specified *Kspring* is in force units. When the climbing replica -is on, :math:`RD_{ideal}` and :math:`meanDist` are calculated separately -each side of the climbing image. Note that the *ideal* form of nudging -can often be more effective at keeping the replicas equally spaced before -climbing, then equally spaced either side of the climbing image whilst -climbing. +case the specified *Kspring* is in force units. When the climbing +replica is on, :math:`RD_{ideal}` and :math:`meanDist` are calculated +separately each side of the climbing image. Note that the *ideal* form +of nudging can often be more effective at keeping the replicas equally +spaced before climbing, then equally spaced either side of the climbing +image whilst climbing. -With a value of *equal* the spring force is computed as for *ideal* -when the climbing replica is off, promoting equidistance. When the climbing +With a value of *equal* the spring force is computed as for *ideal* when +the climbing replica is off, promoting equidistance. When the climbing replica is on, the spring force is computed to promote equidistant -absolute differences in energy, rather than distance, each side of -the climbing image: +absolute differences in energy, rather than distance, each side of the +climbing image: .. math:: @@ -143,23 +143,22 @@ where *ED* is the cumulative sum of absolute energy differences: ED = \sum_{i`. +*meanEdist* is the average absolute energy difference between replicas +up to the climbing image or from the climbing image to the final image, +for images before or after the climbing image +respectively. :math:`ED_{ideal}` is the corresponding cumulative sum of +average absolute energy differences in each case, in close analogy to +*ideal*. This form of nudging is to aid schemes which integrate forces +along, or near to, NEB pathways such as :doc:`fix_pafi `. ---------- -The keyword *perp* specifies if and how a perpendicular nudging force -is computed. It adds a spring force perpendicular to the path in -order to prevent the path from becoming too strongly kinked. It can +The keyword *perp* specifies if and how a perpendicular nudging force is +computed. It adds a spring force perpendicular to the path in order to +prevent the path from becoming too strongly kinked. It can significantly improve the convergence of the NEB calculation when the -resolution is poor. I.e. when few replicas are used; see -:ref:`(Maras) ` for details. +resolution is poor. I.e. when few replicas are used; see :ref:`(Maras) +` for details. The perpendicular spring force is given by @@ -181,10 +180,10 @@ force is added. By default, no additional forces act on the first and last replicas during the NEB relaxation, so these replicas simply relax toward their -respective local minima. By using the key word *end*, additional -forces can be applied to the first and/or last replicas, to enable -them to relax toward a MEP while constraining their energy E to the -target energy ETarget. +respective local minima. By using the key word *end*, additional forces +can be applied to the first and/or last replicas, to enable them to +relax toward a MEP while constraining their energy E to the target +energy ETarget. If :math:`E_{Target} > E`, the interatomic force :math:`F_i` for the specified replica becomes: @@ -197,33 +196,33 @@ specified replica becomes: The "spring" constant on the difference in energies is the specified *Kspring3* value. -When *estyle* is specified as *first*, the force is applied to the -first replica. When *estyle* is specified as *last*, the force is -applied to the last replica. Note that the *end* keyword can be used -twice to add forces to both the first and last replicas. +When *estyle* is specified as *first*, the force is applied to the first +replica. When *estyle* is specified as *last*, the force is applied to +the last replica. Note that the *end* keyword can be used twice to add +forces to both the first and last replicas. For both these *estyle* settings, the target energy *ETarget* is set to the initial energy of the replica (at the start of the NEB calculation). If the *estyle* is specified as *last/efirst* or *last/efirst/middle*, -force is applied to the last replica, but the target energy *ETarget* -is continuously set to the energy of the first replica, as it evolves +force is applied to the last replica, but the target energy *ETarget* is +continuously set to the energy of the first replica, as it evolves during the NEB relaxation. The difference between these two *estyle* options is as follows. When *estyle* is specified as *last/efirst*, no change is made to the -inter-replica force applied to the intermediate replicas (neither -first or last). If the initial path is too far from the MEP, an -intermediate replica may relax "faster" and reach a lower energy than -the last replica. In this case the intermediate replica will be -relaxing toward its own local minima. This behavior can be prevented -by specifying *estyle* as *last/efirst/middle* which will alter the -inter-replica force applied to intermediate replicas by removing the -contribution of the gradient to the inter-replica force. This will -only be done if a particular intermediate replica has a lower energy -than the first replica. This should effectively prevent the -intermediate replicas from over-relaxing. +inter-replica force applied to the intermediate replicas (neither first +or last). If the initial path is too far from the MEP, an intermediate +replica may relax "faster" and reach a lower energy than the last +replica. In this case the intermediate replica will be relaxing toward +its own local minima. This behavior can be prevented by specifying +*estyle* as *last/efirst/middle* which will alter the inter-replica +force applied to intermediate replicas by removing the contribution of +the gradient to the inter-replica force. This will only be done if a +particular intermediate replica has a lower energy than the first +replica. This should effectively prevent the intermediate replicas from +over-relaxing. After converging a NEB calculation using an *estyle* of *last/efirst/middle*, you should check that all intermediate replicas @@ -237,9 +236,10 @@ target energy. Restart, fix_modify, output, run start/stop, minimize info """"""""""""""""""""""""""""""""""""""""""""""""""""""""""" -No information about this fix is written to :doc:`binary restart files `. None of the :doc:`fix_modify ` options -are relevant to this fix. No global or per-atom quantities are stored -by this fix for access by various :doc:`output commands `. +No information about this fix is written to :doc:`binary restart files +`. None of the :doc:`fix_modify ` options are +relevant to this fix. No global or per-atom quantities are stored by +this fix for access by various :doc:`output commands `. No parameter of this fix can be used with the *start/stop* keywords of the :doc:`run ` command. diff --git a/doc/src/neb.rst b/doc/src/neb.rst index 0bc5de010b..d15aa8cd91 100644 --- a/doc/src/neb.rst +++ b/doc/src/neb.rst @@ -89,10 +89,11 @@ potentials, and the starting configuration when the neb command is issued should be the same for every replica. In a NEB calculation each replica is connected to other replicas by -inter-replica nudging forces. These forces are imposed by the :doc:`fix neb ` command, which must be used in conjunction with the -neb command. The group used to define the fix neb command defines the -NEB atoms which are the only ones that inter-replica springs are -applied to. If the group does not include all atoms, then non-NEB +inter-replica nudging forces. These forces are imposed by the +:doc:`fix neb ` command, which must be used in conjunction +with the neb command. The group used to define the fix neb command +defines the NEB atoms which are the only ones that inter-replica springs +are applied to. If the group does not include all atoms, then non-NEB atoms have no inter-replica springs and the forces they feel and their motion is computed in the usual way due only to other atoms within their replica. Conceptually, the non-NEB atoms provide a background @@ -445,7 +446,7 @@ Related commands """""""""""""""" :doc:`prd `, :doc:`temper `, :doc:`fix langevin `, -:doc:`fix viscous ` +:doc:`fix viscous `, :doc:`fix neb ` Default """""""