Test calculations

Since optimisation on lattice variables is time consuming, we have chosen as test cases Ar, KCl and ethane, which are cheap in computer time and yet go through all the new parts of the program. 

---

Quantum chemical methods, exemplified by CASSCF and other MCSCF methods, have now evolved to an extent where it is possible to routinely treat accurately the excited electronic states of molecules containing a number of atoms. Mixed nuclear dynamics, such as swarm of trajectory based surface hopping or Ehrenfest dynamics, or the Gaussian wavepacket based multiple spawning method, use an approximate representation of the nuclear wavepacket based on classical trajectories. They are thus able to use the infoiination from quantum chemistry calculations required for the propagation of the nuclei in the form of forces. These methods seem able to reproduce, at least qualitatively, the dynamics of non-adiabatic systems. Test calculations have now been run using duect dynamics, and these show that even a small number of trajectories is able to produce useful mechanistic infomiation about the photochemistry of a system. In some cases it is even possible to extract some quantitative information. 

The accuracy of the CSP approximation is, as test calculations for model. systems show, typically very similar to that of the TDSCF. The reason for this is that for atomic scale masses, the classical mean potentials are very similar to the quantum mechanical ones. CSP may deviate significantly from TDSCF in cases where, e.g., the dynamics is strongly influenced by classically forbidden regions of phase space. However, for simple tunneling cases it seems not hard to fix CSP, by running the classical trajectories slightly above the barrier. In any case, for typical systems the classical estimate for the mean potential functions works extremely well. 

For many projects, a basis set cannot be chosen based purely on the general rules of thumb listed above. There are a number of places to obtain a much more quantitative comparison of basis sets. The paper in which a basis set is published often contains the results of test calculations that give an indication of the accuracy of results. Several books, listed in the references below, contain extensive tabulations of results for various methods and basis sets. Every year, a bibliography of all computational chemistry papers published in the previous... 

Run test calculations with the new parameters. Then adjust the parameters as necessary to reproduce experimental results before using them to describe an unknown compound. 

The semiempirical techniques available include EH, CNDO, INDO, MINDO/3, ZINDO, MNDO, AMI, and PM3. The ZINDO/S, MNDO/d, and PM3(TM) variations are also available. The semiempirical module seems to be rather robust in that it did well on some technically difficult test calculations. 

The ah initio module can run HF, MP2 (single point), and CIS calculations. A number of common basis sets are included. Some results, such as population analysis, are only written to the log file. One test calculation failed to achieve SCF convergence, but no messages indicating that fact were given. Thus, it is advisable to examine the iteration energies in the log file. 

The object of the code is to detail the test to determine the power output and thermal efficiency of the gas turbine when operating at the test conditions, and correcting these test results to standard or specified operating and control conditions. Procedures for conducting the test, calculating the results, and making the corrections are defined. 

We ve included only one additional keyword, Test, which says this is a test calculation whose results should not be entered into the Gaussian archive (if used at your site). 

Another method that may be employed to test whether single data points should be included in a sample mean is the Q-test. This simple test determines the confidence with which a data point can or cannot be considered part of the data set. The test calculates a ratio of the gap between the data point and its nearest neighbor and the range of the complete data set ... 

Output Tests, Calculated Explosion Temperatures, and Results of... 

Experimental observations and test calculations pointed out a special behaviour of the nitrate anion when faced with 6arbocations. Therefore a detailed investigation with the assistance of the MINDO/3 and the Huron-Claverie method was carried out122). It appeared that in addition to the ester formation and the proton transfer to the counterion, the formation of NO+ by oxygen transfer to the cation must be considered as well (see Fig. 11). 

Since no experimental work is available to confront the theoretical model designed to describe C3H2 excited states correctly, test calculations had to be done in a preliminary step. For that purpose, we have chosen ethylene, for which extensive calculations of the vertical spectrum as well as experimental measures are available. It is well known indeed that a correct quantitative and even qualitative description of small rr-electronsystems, is still a challenge for theoretical chemistry. The difficulties are found at each step of the computational approach ... 

I. Test Calculations on Transition-Metal Carbonyls , Int. J. Quant. Chem., 58, 147. 

In the next section, we show an example of test calculations of the three-layer ONIOM method. 

When the FMS method was first introduced, a series of test calculations were performed using analytical PESs. These calculations tested the numerical convergence with respect to the parameters that define the nuclear basis set (number of basis functions and their width) and the spawning algorithm (e.g., Xo and MULTISPAWN). These studies were used to validate the method, and therefore we refrained from making any approximations beyond the use of a... 

Priputina I., Abramychev, A., Lukjanov, A., Mikhailov, A. (2004b). Test calculations of critical loads for Pb and Cd results from key plots studies in European Russia. In Proceedings of 6th Subregional Meeting of ICPs and Training Workshop on the Calculation and Mapping of Critical Loads for Air Pollutants Relevant for UN/ECE Convention on LRTAP in East and South East European Countries. Moscow-Pushchino, pp. 66-74. 

The original derivation of the P3 method was accompanied by test calculations on challenging, but small, closed-shell molecules with various basis sets [12], The average absolute error was approximately 0.2 eV... 

Test Calculations on H3 and Geometry Optimization Extension to Non-Born-Oppenheimer Discussion... 

In order to find a reasonable configuration for our calculation, we take test calculation to optimize the bulk structure of pyrite with GGA and LDA exchange-correlation functional. In the calculation, the plane wave cutoff energy set is 280 eV and the key point set is 4 x 4 x 4, the convergence tolerances set is 10 eV/atom. The optimized cell parameter of the two methods is 0.5415 nm and 0.5425 nm respectively, which is in good agreement with the experiment data (0.5417 nm) reported. It indicates that this configuration is sufficient to satisfy the request of accuracy. 

The most important ZnS surface is the (110), which is the most common growth surface and is also the perfect cleavage surface. Therefore, the calculation is based on the ZnS (110) surface. The surfaces are cleaved from the bulk ZnS with the optimtun tinit cell volume determined using the GGA with CASTER The Cu and Fe doped surfaces are built by the substitution of Cu or Fe for Zn atom on the cleaved surface. A vacuum spacing of 1.5 nm is inserted in the z-direction to form a slab and mimic a 2D surface. In order to eliminate the interactions between mirror images in the z-direction due to the periodic boimdary conditions, in test calculations, we have done some total energy calculation to find a proper thickness of slab. The result shows that 1.5 run is a desirable thickness. 

---