Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: MOLPOP-CEP: An Exact, Fast Code for Multi-Level Systems   We present MOLPOP-CEP, a universal line transfer code that allows the exact
calculation of multi-level line emission from a slab with variable physical
conditions for any arbitrary atom or molecule for which atomic data exist. The
code includes error control to achieve any desired level of accuracy, providing
full confidence in its results. Publicly available, MOLPOP-CEP employs our
recently developed Coupled Escape Probability (CEP) technique, whose
performance exceeds other exact methods by orders of magnitude. The program
also offers the option of an approximate solution with different variants of
the familiar escape probability method. As an illustration of the MOLPOP-CEP
capabilities we present an exact calculation of the Spectral Line Energy
Distribution (SLED) of the CO molecule and compare it with escape probability
results. We find that the popular large-velocity gradient (LVG) approximation
is unreliable at large CO column densities. Providing a solution of the
multi-level line transfer problem at any prescribed level of accuracy,
MOLPOP-CEP is removing any doubts about the validity of its final results.

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The categories of this paper are: math
32
The categories of this paper are: atom-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: solv-int
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The categories of this paper are: quant-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: nucl-th
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The categories of this paper are: cond-mat
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The categories of this paper are: adap-org
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The categories of this paper are: q-fin
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The categories of this paper are: plasm-ph
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The categories of this paper are: physics
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The categories of this paper are: supr-con
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The categories of this paper are: eess
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The categories of this paper are: hep-lat
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The categories of this paper are: cs