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= bdfopt =

<<TableOfContents(4)>>

== Introduction ==

Geometry optimiser of BDF package.  This BDFOPT module can be used to find minimal points, saddle points and also conical intersection points. For details of the interface, see '''bdfopt/''', '''module/bdfopt_mod.F90,dlfind_module.F90''', '''sys_util/bdf_dlfind_util.F90''' for interface.

Two optimizers can be used by specify the '''solver''' keywords:

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 using internal coordinates.

The optimization information is stored in filename.pes1 [ground state/excited state] or filename.pes2 [conical intersection].

Currently, the following methods are available:

1. HF/MCSCF with GRAD module

2. HF/DFT/TD-DFT with RESP modules

== 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]]

== 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