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= bdfopt =

<<TableOfContents(4)>>

== Introduction ==

Geometry optimiser of BDF package.  Two optimizers can be used:

1. Interface to DL-FIND. For details, see: http://ccpforge.cse.rl.ac.uk/gf/project/dl-find/

"DL-FIND: An Open-Source Geometry Optimizer for Atomistic Simulations", Johannes Kästner, Joanne M. Carr, Thomas W. Keal, Walter Thiel, Adrian Wander and Paul Sherwood, J. Phys. Chem. A, 2009, 113 (43), 11856-11865. DOI: 10.1021/jp9028968
 
2. Original optimizer in BDF developed by Dr. Yong Zhang.

This BDFOPT module can be used to find minimal points, saddle points and also conical intersection points, when combined with TD-DFT and RESP modules.
For details of the interface, see '''bdfopt/''', '''module/bdfopt_mod.F90,dlfind_module.F90''', '''sys_util/bdf_dlfind_util.F90''' for interface.

== Current limitations ==

This preliminary version has several limitations:

1. Change of symmetry during optimization is not correctly handled for excited state optimization, because the correct input file needs to be prepared.

2. Conical intersection optimization does not work properly!

3. Since RESP only support nonrelativistic calculations currently, spin-free X2C based approach can not be used in optimization [to be changed in future].

== Examples ==

1. [[Ground-state opt]]

2. [[ Excited state opt ]]

3. [[ Conical intersection with pp-TDA ]]

== General keywords ==
=== IPRT ===

=== SOLVER ===
=0, DLFIND; =1, BDF optimizer

=== MAXCYCLE ===

=== TOLGRAD ===

=== TOLENE ===

=== IOPT ===
Algorithm for optimization, default L-BFGS

=== ICOORD ===
Coordinates

=== IMULTI ===
multi-state optimization for conical intersection

=== ILINE ===
line search