I used 'sentimental fiction' in it's sense of being a genre of literary fiction. My definition of sentimental fiction would be 'a genre that explores inter-personal ethics within a wider socio-political context and/or develops/explores the language humans have for experiencing this'.
Sentimental novels include the work of Jane Austen and Laurence Sterne.
It's arguable that it might include Antonio Di Masio and even Jacqueline Rose's work on political identification.
There was a post-Victorian move to identify 'sentiment' and 'sentimental novels' as gushy, mimsy, over-emotional, irrational nonsense, penned by women. I think you can spot the gender bias in that characterisation.
There remains, I think, a similar devaluing of the term 'sentiment' and 'sentimental fiction' to this day.
I, personally, think those dynamics exist in 'Atonement' - unconsciously. I think the novel sets out to explore those issues (it is within the genre of sentimental fiction) but actually reproduces that sexist dynamic.
Eg. McKewan, ourC20 male hero, 'undoes' the preconceptions of sentimental fiction by including rape, child abuse, child sexuality, post-modern elements: supposedly shocking and challenging our understanding of the parameters of sentimental fiction.
The female author reproduces them, sanitises life's nastiness, adds collusive fantasies of consolatory romance, lies in her (fictional) sentimental novel(s).
Personally, I think that is a sexist recuperation of the work of many feminist critics to open out and reclaim the work of (primarily female) authors of sentimental fiction.
He kind of 'grabs' all the modern reinterpretations of sentimental fiction for 'the masculine' whilst simultaneously off-loading the (still!) negative elements onto an imaginary feminine.
It annoys me because I read it as a land grab by a male author of the work of primarily female and feminist literary critics.