bdfopt

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 specifying the solver keyword:

1. [solver=1] Original optimizer in BDF developed by Dr. Yong Zhang using redundant internal coordinates (more efficient!).

2. [solver=0] Interface to the package - 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

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

3. TD-DFT find minimal points, first-order saddle points (TS), Conical intersection (CI) and intersystem crossing (ISC) points.

4. CASSCF find minimal points, first-order saddle points (TS), Conical intersection (CI) and intersystem crossing (ISC) points.

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.

Examples

1. Ground-state opt

2. Excited state opt

3. Conical intersection

General keywords

IPRT

Print level.

SOLVER

=0, DLFIND; =1, BDF optimizer

MAXCYCLE

Maximum number of iterations.

TOLGRAD

Convergence criterium for RMS gradient.

TOLENE

Convergence criterium for energy change (only supported for solver=0).

TOLSTEP

Convergence criterium for RMS step (only supported for solver=1).

IOPT

3: search for minima using RFO step
10: search for saddle points using P-RFO step

Default: 3

TRUST

Specify the initial trust radius (unit: Bohr). The trust radius will be dynamically updated (either increased, decreased, or left unchanged) by the program at each geometry optimization iteration. If a negative value r is specified, the initial trust radius is set as |r|, and the trust radius will remain no larger than |r| throughout the geometry optimization. This is useful when a very small trust radius is needed but the dynamic update scheme somehow does not realize this and keeps increasing the trust radius. Default: 0.3

UPDATE

Algorithm for Hessian update.

0: calculate numerical Hessian at every step
1: Powell update for saddle points (solver=0 only)
2: Bofill update for saddle points
3: L-BFGS update (solver=0) or BFGS update (solver=1)
9: Bofill update for minima

If update is not 0, a molecular mechanics Hessian will be built at the first step of the geometry optimization. Default: 3

ICOORD

0: Cartesian coordinates (ignored if solver=1, since the BDF solver can only use redundant internal coordinates)
1: Redundant internal coordinates

NONCOUPL

with this keyword,interstate coupling gradient calculation is not employed to ISC optimization.

IMULTI

multi-state optimization for conical intersection (CI) and intersystem crossing(ISC).

0: no multi-state optimization (default)

1: Penalty function method optimize CI and ISC without neither nonadiabatic coupling and interstate coupling gradient calculations.

2: Gradient projection method optimize CI and ISC; CI optimization needs nonadiabatic coupling (default), ISC optimization require set keyword 'Noncoupl' to skip interstate coupling gradient calculation.

ILINE

0: do not do line search (default for solver=0)
1: do line search (default for solver=1)

CONSTRAIN

Invokes constrained optimization.
The first line after the keyword is the number of constraints, N. The 2nd to (N+1)th lines each consists of 2 to 4 integers, which are to be interpreted as atomic serial numbers.
If 2 integers are given, then the bond between the two atoms is frozen.
If 3 integers are given, then the angle between the three atoms is frozen.
If 4 integers are given, then the dihedral between the four atoms is frozen.

HESS

Calculates numerical Hessian. The following line must be one of the following four keywords:

only
   calculates the numerical Hessian without performing a geometry optimization. This also gives the vibrational frequencies, vibrational modes, and thermochemical functions such as ZPE, inner energy, enthalpy, entropy and Gibbs free energy.

init
   calculates the numerical Hessian, then performs geometry optimization using the Hessian as the initial Hessian. This is useful for transition state optimizations, where the default molecular mechanics Hessian is of poor quality. The vibrational frequency and thermochemistry analyses are not performed.

final
   does geometry optimization, and if the geometry optimization converges, calculates the numerical Hessian at the converged structure. The vibrational frequency and thermochemistry analyses are performed.

init+final
   calculates the Hessian both before and after geometry optimization. The vibrational frequency and thermochemistry analyses are performed on the final Hessian, but not on the initial Hessian.

To save computational costs, Hessians whose only role is to aid geometry convergence are calculated using single-sided finite difference. Otherwise, two-sided finite difference is used, which provides better accuracy. The computed Hessian is stored in $BDFTASK.hess, where $BDFTASK is the name of the input file with the extension .inp stripped off.

NUMHESSSTEP

Step length used in the finite-difference numerical Hessian procedure (unit: Bohr). Default: 0.001.

RECALCHESS

The next line must be an integer, x. The numerical Hessian is recalculated every x geometry optimization steps.

RESTARTHESS

Resume an aborted numerical Hessian job.

READHESS

Read $BDFTASK.hess as the initial Hessian for geometry optimization. This is especially useful for transition state optimizations where the initial Hessian is intended to be computed at a lower level.

NDEG

Degree of degeneracy of the electronic wavefunction (used in computation of electronic entropy). Equals to 2S+1 for scalar states whose spatial parts belong to nondegenerate irreps; can acquire or lose degeneracy if non-Abelian point group symmetry or spin-orbit coupling are present. Default: 1. Note: NDEG must be given explicitly whenever it is not 1, even if its value is apparent from the rest of the input file!

TEMP

Temperature used in themochemistry analysis (in Kelvin). Default: 298.15.

PRESS

Pressure used in themochemistry analysis (in atm). Default: 1.

SCALE

Scale factor of harmonic frequencies. Default: 1.0.