Wave function, electronic excited state

To use direct dynamics for the study of non-adiabatic systems it is necessary to be able to efficiently and accurately calculate electronic wave functions for excited states. In recent years, density functional theory (DFT) has been gaining ground over traditional Hartree-Fock based SCF calculations for the treatment of the ground state of large molecules. Recent advances mean that so-called time-dependent DFT methods are now also being applied to excited states. Even so, at present, the best general methods for the treatment of the photochemistry of polyatomic organic molecules are MCSCF methods, of which the CASSCF method is particularly powerful. 

The greater the number of functions 4 J, belonging to the orthonormal set, the more completely and in more detail the spectrum of the /(-decay-induced excitations of a molecule can be calculated. Consequently, the method for calculating the wave functions of the daughter ion must be such that at a reasonable volume of calculation we would be able to construct a sufficiently large number of multielectron wave functions of excited states. The Hartree Fock method allows one to construct the wave functions of excited states as the combinations of determinants symmetrized in a certain way. Within this method the excitation is considered to be a transition of an electron from an occupied Hartree-Fock molecular orbital into a vacant one. 

CIS calculations from the semiempirical wave function can be used for computing electronic excited states. Some software packages allow Cl calculations other than CIS to be performed from the semiempirical reference space. This is a good technique for modeling compounds that are not described properly by a single-determinant wave function (see Chapter 26). Semiempirical Cl... 

This is an introduction to the techniques used for the calculation of electronic excited states of molecules (sometimes called eximers). Specifically, these are methods for obtaining wave functions for the excited states of a molecule from which energies and other molecular properties can be calculated. These calculations are an important tool for the analysis of spectroscopy, reaction mechanisms, and other excited-state phenomena. 

Q-Chem also has a number of methods for electronic excited-state calculations, such as CIS, RPA, XCIS, and CIS(D). It also includes attachment-detachment analysis of excited-state wave functions. The program was robust for both single point and geometry optimized excited-state calculations that we tried. 

You can use Cl to predict electronic spectra. Since the Cl wave function provides ground state and excited state energies, you can obtain electronic absorption frequencies from the differences between the energy of the ground state and the excited states. 

We have presented a practical Hartree-Fock theory of atomic and molecular electronic structure for individual electronically excited states that does not involve the use of off-diagonal Lagrange multipliers. An easily implemented method for taking the orthogonality constraints into account (tocia) has been used to impose the orthogonality of the Hartree-Fock excited state wave function of interest to states of lower energy. 

Both minima and saddle points are of interest. In the case of wave functions, the ground state is a minimum and the excited states are saddle points of the electronic energy function.6 On potential surfaces minima and first-order saddle points correspond to equilibrium geometries and transition states. Higher-order saddle points on potential energy surfaces are of no interest. 

The calculation of a point on a potential-energy hypersurface is equivalent to calculating the energy of a diatomic or polyatomic system for a specified nuclear configuration and thus presents considerable practical computational difficulty. For certain problems or nuclear configurations, the maximum possible accuracy is needed, and under these conditions relatively elaborate ab initio methods are indicated. For other problems, the description to a uniform accuracy of many electronically excited states of a given system is required. Such is the situation for the atmospheric systems described here, and thus most of our final potential curves are based on the analysis of VCI wave functions constructed to uniform quality for representation of the excited states. 

In molecular crystals the forces between molecules are much smaller than those within molecules. It is for this reason adequate in dealing with the low electronically excited states to use the free-molecule wave functions and to treat crystal perturbations on them only in a higher approximation. Accordingly we shall denote by q>, y1, q ,.. ., electronic states of the free molecules, and show by subscripts (i,j) the location of the chosen molecule in the crystal. In a crystal of N molecules with h in each unit cell, the complete set of molecules is contained in the product wave function... 

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