Optimization Examples - Open-Quantum-Platform/openqp GitHub Wiki

[input]
system=
   O  -0.0000000000   0.0000000000  -0.0410615540
   H  -0.5331943294   0.5331943294  -0.6144692230
   H   0.5331943294  -0.5331943294  -0.6144692230
charge=0
functional=bhhlyp
basis=6-31g*
runtype=optimize
method=hf

[scf]
type=rhf
multiplicity=1

[optimize]
istate=0

[input] Section

• system: This is the coordination of your system, your system's coordination can be achieved through two primary methods for OQP. The first method employs the Standard Cartesian format, as illustrated in the provided example. The second method utilizes the .XYZ format. To leverage the .XYZ format, save your coordination details in this format within your input folder, for instance, as H2O.xyz. Subsequently, it can be easily applied by specifying system=H2O.xyz in your input file. Here is an example of .XYZ format:

3
symmetry c1
O        0.000000000      0.000000000     -0.041061554
H       -0.533194329      0.533194329     -0.614469223
H        0.533194329     -0.533194329     -0.614469223

• charge: The total charge of the system. A value of 0 indicates that the molecule is neutral, with no net charge.

• runtype: Set to optimize, indicating the goal is to perform a geometry optimization. This process iteratively adjusts the molecular geometry to find the structure that minimizes the system's total energy.

• basis: The basis set used for the calculation, 6-31gs in this case. The 6-31gs is a split-valence basis set with polarization functions on heavy atoms, designed to provide a good balance between accuracy and computational cost. You can find all of the basis-sets supported by OQP within the basis_set folder.

#----------------------------------------------------------------------
# Basis Set Exchange
# Version v0.9.1
# https://www.basissetexchange.org
#----------------------------------------------------------------------
#   Basis set: 6-31+G*
# Description: 6-31G + diffuse and polarization functions on heavy
#                    atoms
#        Role: orbital
#     Version: 1  (Data from Gaussian 09/GAMESS)
#----------------------------------------------------------------------



# HYDROGEN
S   H
      0.3349460434E-01       0.1873113696E+02
      0.2347269535E+00       0.2825394365E+01
      0.8137573261E+00       0.6401216923E+00
S   H
      1.0000000              0.1612777588E+00

# OXYGEN
S   O
      0.1831074430E-02       0.5484671660E+04
      0.1395017220E-01       0.8252349460E+03
      0.6844507810E-01       0.1880469580E+03
      0.2327143360E+00       0.5296450000E+02
      0.4701928980E+00       0.1689757040E+02
      0.3585208530E+00       0.5799635340E+01
L   O
     -0.1107775495E+00       0.1553961625E+02       0.7087426823E-01
     -0.1480262627E+00       0.3599933586E+01       0.3397528391E+00
      0.1130767015E+01       0.1013761750E+01       0.7271585773E+00
L   O
      0.1000000000E+01       0.2700058226E+00       0.1000000000E+01
L   O
      0.1000000000E+01       0.8450000000E-01       0.1000000000E+01
D   O
      1.0000000              0.8000000000E+00

• functional: Specifies the DFT functional to be used. bhhlyp is a hybrid functional that combines Hartree-Fock exchange with B88 exchange and LYP correlation. It's known for its good performance in a variety of systems.

• method: Indicates that the Hartree-Fock (HF) method will be used. However, the specification of a DFT functional (bhhlyp) suggests that the calculation will incorporate DFT principles, which is indicating a hybrid approach. In practice, HF calculations do not use a functional, so this setup is aim to use RHF as the basis for a DFT calculation, combining the two methodologies.

[scf] Section

• multiplicity: A multiplicity of 1 indicates a singlet state, which is typical for the ground state of closed-shell molecules like water, implying all electrons are paired.

• type: The rhf (Restricted Hartree-Fock) method is selected for the SCF calculations. RHF is appropriate for singlet state systems and assumes all electrons are spin-paired, providing a wave function that is an eigenfunction of the total spin operator.

[optimize] Section

• istate: Specifies that the optimization should be performed for the ground state (istate=0). This parameter ensures the geometry optimization targets the molecule's lowest energy structure, essential for studying stable molecular configurations and properties.

[input]
system=
   O  -0.0000000000   0.0000000000  -0.0410615540
   H  -0.5331943294   0.5331943294  -0.6144692230
   H   0.5331943294  -0.5331943294  -0.6144692230
charge=0
functional=bhhlyp
basis=6-31g*
runtype=optimize
method=tdhf

[scf]
type=rohf
multiplicity=3

[tdhf]
type=mrsf
nstate=2

[optimize]
istate=1

[input] Section

• method: Indicates the computational method, tdhf for time-dependent Hartree-Fock.

[scf] Section

• multiplicity: The multiplicity of the system, given by 2S+1 where S is the total spin angular momentum. A multiplicity of 3 suggests a triplet state (S=1), indicating unpaired electrons and a potentially open-shell configuration.

• type: The SCF calculation type, rohf for Restricted Open-Shell Hartree-Fock. ROHF methods are used for molecules with open-shell electronic configurations, providing a way to handle both closed-shell (paired electrons) and open-shell (unpaired electrons) components of the wavefunction.

[tdhf] Section

• type: The type of time-dependent calculation, mrsf for mixed-reference spin-flip. This advanced approach is designed to accurately describe excited states, particularly those involving changes in electron spin states. It allows for the treatment of systems where single-reference methods might fail, especially for complex excited-state phenomena.

• nstate: The calculation will consider two electronic states, likely including the ground state and the first excited state, allowing for an exploration of the molecule's electronic landscape.

[optimize] Section

• istate: Specifies that the optimization is to be performed for the first excited state (istate=1, assuming the ground state is indexed as 0).

[input]
system=
 C       -1.795088763      0.000123456     -1.451300047
 C       -1.795088763      0.000006782     -0.121142047
 H       -1.814929585      0.922236408     -2.025683763
 H       -1.788852366     -0.923335017     -2.024225748
 H       -1.807520960      0.923298955      0.451740825
 H       -1.790072549     -0.927319218      0.445324378
runtype=mep
functional=bhhlyp
charge=0
method=tdhf
basis=6-31g*

[scf]
type=rohf
maxit=50
multiplicity=3

[tdhf]
type=mrsf
nstate=5

[optimize]
optimizer=bfgs
maxit=100
mep_maxit=2
istate=2
energy_shift=1e-3
step_size=0.1
step_tol=0.01
rmsd_grad=3e-3
max_grad=5e-3

[input] Section

• runtype: Set to mep, indicating that the calculation aims to find the Minimum Energy Path, a crucial aspect of exploring reaction mechanisms and energy barriers between states.

[scf] Section

• maxit: Sets the maximum number of iterations for the SCF procedure to 50, ensuring the electronic structure converges to a stable solution.

[tdhf] Section

• nstate: Considers five states in the calculation, likely including the ground state and four excited states, to comprehensively explore the system's electronic landscape.

[optimize] Section

• optimizer: Chooses bfgs(Broyden–Fletcher–Goldfarb–Shanno algorithm), a robust optimization algorithm well-suited for finding local minima in complex potential energy surfaces.

• maxit: Specifies the maximum number of optimization iterations as 100, allowing for extensive exploration of the energy landscape.

• mep_maxit: Limits the MEP calculation iterations to 2, focusing the search on connecting the specified states efficiently.

• istate: Targets the second excited state (istate=2) for the MEP calculation, aiming to explore the transition pathway from this specific state.

• energy_shift, step_size, step_tol, rmsd_grad, max_grad: These parameters fine-tune the optimization process, adjusting the energy criteria, step sizes, and convergence thresholds to ensure accurate and efficient mapping of the Minimum Energy Path.

[input]
system=
 C          -1.6699351346837055       0.1537249235528157      -1.5459803491111643
 C          -1.8079415266835852      -0.0386075716896284      -0.1602069788110266
 H          -2.6609567768367581       0.2572290722092156      -2.0290359598415040
 H          -1.2898503996116444      -0.7568524635289917      -2.0470428696820342
 H          -1.3096398768036397       0.6557118321425524       0.5396052278505126
 H          -2.3820842951209360      -0.7983813277099963       0.4308517619153288
runtype=meci
functional=bhhlyp
charge=0
method=tdhf
basis=6-31g*

[scf]
type=rohf
maxit=50
multiplicity=3

[tdhf]
type=mrsf
nstate=5

[optimize]
optimizer=bfgs
maxit=50
istate=1
jstate=2
energy_shift=1e-5
energy_gap=1e-4
rmsd_grad=5e-4
max_grad=1e-3

[input] Section

• runtype: Set to meci, indicating that the calculation aims to find a Minimum Energy Conical Intersection, a key feature in the study of excited-state dynamics and photochemistry.

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