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| spcat-considerations [2024/07/12 15:21] – mueller | spcat-considerations [2024/07/15 14:45] (current) – [Considerations for the intensity cutoffs] mueller | ||
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| FLAGS, TAG, QROT, FBGN, FEND, STR0, STR1, FQLIM, TEMP\\ | FLAGS, TAG, QROT, FBGN, FEND, STR0, STR1, FQLIM, TEMP\\ | ||
| \\ | \\ | ||
| - | * FLAGS: the most important ones are **0** for a short output file without energy file | + | * **FLAGS**: the most important ones are **0** for a short output file without energy file |
| and **1** for the calculation of an energy file in addition. If all of your frequencies **and** | and **1** for the calculation of an energy file in addition. If all of your frequencies **and** | ||
| parameter values are in units of inverse centimeters, | parameter values are in units of inverse centimeters, | ||
| Line 40: | Line 40: | ||
| in front of the uncertainty.\\ | in front of the uncertainty.\\ | ||
| - | * TAG: The tag is used in a catalog file to identify a species. Up to six characters may be used. | + | * **TAG**: The tag is used in a catalog file to identify a species. Up to six characters may be used. |
| The first up to three digits in the CDMS reprsent the molecular weight of the molecule in atomic mass units, | The first up to three digits in the CDMS reprsent the molecular weight of the molecule in atomic mass units, | ||
| next come a 5, and two digits for counting.\\ | next come a 5, and two digits for counting.\\ | ||
| - | * QROT is the value of the partition function at the desired temperature. The default temperature is 300 K. | + | * **QROT** is the value of the partition function at the desired temperature. The default temperature is 300 K. |
| Considerations for **Evaluating the partition function** are given separately below.\\ | Considerations for **Evaluating the partition function** are given separately below.\\ | ||
| - | * FBGN is the //F// (or //J// or //N//) value at which the calculation should start.\\ | + | * **FBGN** is the //F// (or //J// or //N//) value at which the calculation should start.\\ |
| - | * FEND is the //F// (or //J// or //N//) value at which the calculation should end.\\ | + | * **FEND** is the //F// (or //J// or //N//) value at which the calculation should end.\\ |
| **Please note:** While your calculation usually should start at 0, you may want to run | **Please note:** While your calculation usually should start at 0, you may want to run | ||
| only a partial forward calculation if you are interested in a subset of transitions. | only a partial forward calculation if you are interested in a subset of transitions. | ||
| Line 55: | Line 55: | ||
| below.\\ | below.\\ | ||
| - | * STR0 is the first cutoff value of the decadic logarithm of the intensity in the intensity units | + | * **STR0** is the first cutoff value of the decadic logarithm of the intensity in the intensity units |
| employed in the catalog file. It is applied linearly!\\ | employed in the catalog file. It is applied linearly!\\ | ||
| - | * STR1 is the second cutoff value of the decadic logarithm of the intensity in the intensity units | + | * **STR1** is the second cutoff value of the decadic logarithm of the intensity in the intensity units |
| employed in the catalog file. Basically, the intensity **Int** has to fulfil the following: | employed in the catalog file. Basically, the intensity **Int** has to fulfil the following: | ||
| \\ | \\ | ||
| Line 66: | Line 66: | ||
| \\ | \\ | ||
| - | * FQLIM is the upper frequency limit in units of gigahertz.\\ | + | * **FQLIM** is the upper frequency limit in units of gigahertz.\\ |
| \\ | \\ | ||
| - | * TEMP is the temperature. The default value is 300 K. **Any** other temperature may be chosen | + | * **TEMP** is the temperature. The default value is 300 K. **Any** other temperature may be chosen |
| as long as the partition function value may be evaluated at this temperature.\\ | as long as the partition function value may be evaluated at this temperature.\\ | ||
| \\ | \\ | ||
| Line 88: | Line 88: | ||
| ==== Evaluating the partition function ==== | ==== Evaluating the partition function ==== | ||
| - | \\ | + | SPCAT calculates the partition function by default at the temperatures of |
| - | + | 300, 225, 150, 75, 37.5, 18.75, and 9.275 K by direct summation of the contributions | |
| + | of quantum levels as specified in the intensity and variance files. | ||
| + | Other temperatures will be calculated individually as specified by TEMP in the intensity file. | ||
| + | Therefore, it is of utmost importance to take a number of aspects into account.\\ | ||
| + | \\ | ||
| + | * **FBGN** should be set to 0 or the lowest allowed value.\\ | ||
| + | \\ | ||
| + | * **FEND** should be chosen high enough, such that the value of **QROT** at the highest temperature | ||
| + | is converged with respect to the quoted digits. Please note: while it may be fine to choose a value | ||
| + | higher than necessary, we recommend strongly to avoid values too high by far as peculiarities may occur | ||
| + | at very high //K// values, in particular at very high //J//.\\ | ||
| + | \\ | ||
| + | * It is **very** important to take care that the energy of the lowest allowed hyperfine state is at zero energy! | ||
| + | This is particular important in cases of large spin-orbit splitting where the energy of the **unsplit** | ||
| + | //N// = 0 level will be at energy 0 without any modification! The energies will be too low as a consequence! | ||
| + | On the other hand, if you start your calculation of, e.g., H< | ||
| + | the //J// = //K// = 0 level at 0, your energies will be too high!\\ | ||
| + | \\ | ||
| + | * If you are fitting multiple isotopologs or one isotopolog with several degrees of hyperfine splitting, | ||
| + | you should set the weights (WTPL and WTMN) of all unwanted " | ||
| + | \\ | ||
| + | * The **maximum //K//** value in the variance file should be high enough, such that the value of **QROT** | ||
| + | at the highest temperature is converged with respect to the quoted digits. See also the respective remark | ||
| + | for **FEND**.\\ | ||
| + | \\ | ||
| + | * If you need to take into consideration excited vibrational states, and you do not have sufficient | ||
| + | accurate information on excited vibrational states, it will be best to determine only // | ||
| + | analytically and apply // | ||
| + | \\ | ||
| ==== Considerations for the intensity cutoffs ==== | ==== Considerations for the intensity cutoffs ==== | ||
| - | \\ | + | It is very important to choose a reasonable temperature first. If you have more than one, |
| + | it is useful to determine the intensity cutoffs separately for each case, unless | ||
| + | the temperatures differ only marginally. | ||
| + | **STR0** should be chosen low enough that at least the //J// = 1 − 0 transitions show up in the catalog file. | ||
| + | In the case of molecules in cold environments or if your experimental rotatational temperature is low | ||
| + | and // | ||
| + | the //J// = 1 − 1 transitions show up in the catalog file. | ||
| + | **STR1** should be chosen high enough that not too many transitions with large uncertainties occur | ||
| + | in the catalog file, unless you do want this. | ||
| + | **Please note:** If the line list is relatively small with respect to the parameter set, | ||
| + | it may be useful to calculate to a value **FEND** that is much smaller than the one to | ||
| + | calculate the partition function properly. You can have multiple option lines in your | ||
| + | intensity file after the dipole moments lines and after one blank line. | ||
| + | Just exchange the desired line with the one that is currently in row 2. | ||
| + | Please note also that you may have to balance **STR0** and **STR1** to obtain | ||
| + | a recent catalog output, in particular in cases, in which the two values differ very much. | ||
| + | In rarer cases, it may be useful to have **STR1** < **STR0**, mainly if you want to | ||
| + | have frequencies well beyond the Boltzmann peak at the desired frequency. | ||
| + | In most cases, you will find that it is useful to have **STR0** < **STR1**. | ||
| + | \\ | ||